#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <sstream>
#include <map>
#include <set>
#include <queue>
#include <vector>

using namespace std;

#define FOR(prom, a, b) for(int prom = (a); prom < (b); prom++)
#define FORD(prom, a, b) for(int prom = (a); prom > (b); prom--)
#define FORDE(prom, a, b) for(int prom = (a); prom >= (b); prom--)

#define DRI(a) int a; scanf("%d ", &a);
#define DRII(a, b) int a, b; scanf("%d %d ", &a, &b);

#define RI(a) scanf("%d ", &a);
#define RII(a, b) scanf("%d %d ", &a, &b);

#define PB push_back
#define MP make_pair

#define ll long long
#define ull unsigned long long

#define MM(co, cim) memset((co), (cim), sizeof((co)))

#define DEB(x) cerr << ">>> " << #x << " : " << x << endl;
/*
int a[1000014], n = 1000007;

struct line {
  int y1, y2, x1, x2;
  bool begin;
  bool operator<(const line& a) const {
    if(hor() && a.hor()) {
      if(begin && a.begin) {
        return x1 < a.x1;
      } else if(begin) {
        return x1 < a.x2;
      } else if(a.begin) {
        return x2 < a.x1;
      } else {
        return x2 < a.x2;
      }
    } else if(hor() && !a.hor()) {
      if(begin) {
        return x1 < a.x1;
      } else {
        return x2 <= a.x1;
      }
    } else if(!hor() && a.hor()) {
      if(a.begin) {
        return x1 <= a.x1;
      } else {
        return x1 < a.x2;
      }
    } else {
          if(x1 != a.x1) return x1 < a.x1;
    }
  }
  bool hor() const {
    if(y1 == y2) return true;
    return false;
  }
};

struct cord {
  int real;
  int idx;
  bool operator<(const cord& a) const {
    return real < a.real;
  }
};

int read(int idx) {
  int sum = 0;
  while(idx >= 0) {
    sum += a[idx];
    idx = (idx & (idx+1)) - 1;
  }
  return sum;
}

void update(int idx, int val) {
  while(idx < n) {
    a[idx] += val;
    idx |= (idx+1);
  }
}

int X[1000007];
int Y[1000007];

set<line> lns;

set<cord> mpx;
set<cord> mpy;
*/

// OMG ty kokot

int A[1000007];

int main ()
{
  int N;
  while(cin >> N) {
    FOR(i,0,N) RI(A[i]);
    
    bool poss;
    int W, W2, H, H2, d;
    // ven
    
    int mx = 0;
    W = H = 0;
    W2 = H2 = 0;
    d = 0;
    poss = true;
    FOR(i,0,N) {
      switch(d) {
        case 0:
          if(A[i] <= H) {
            poss = false;
            mx = max(mx,i);
            H = A[i];
            W = W - W2;
            break;
          }
          H2 = H;
          H = A[i];
          break;
        case 1:
          if(A[i] <= W) {
            poss = false;
            mx = max(mx,i);
            break;
          }
          W2 = W;
          W = A[i];
          break;
      }
      d++;
      d %= 2;
      if(!poss) break;
    }
    if(poss) {
      cout << "OK" << endl;
      continue;
    }
    poss = true;
    FOR(i,mx+1,N) {
      switch(d) {
        case 0:
          if(A[i] >= H) {
            poss = false;
            mx = i;
            break;
          }
          H = A[i];
          break;
        case 1:
          if(A[i] >= W) {
            poss = false;
            mx = i;
            break;
          }
          W = A[i];
          break;
      }
      d++;
      d %= 2;
      if(!poss) break;
    }
    if(poss) {
      cout << "OK" << endl;
      continue;
    }
    cout << mx << endl;
  }
  return 0;
}

/*
    bool poss = true;
    int mx = 0;
    int W = 1000000007, H = 1000000007;
    int d = 0;
    FOR(i,0,N) {
    }
    //cout << mx << endl;
    if(poss) {
      cout << "OK" << endl;
      continue;
    }
    cout << mx << endl;
  }
    /*
    n = N+5;
    int d = 0, x = 0, y = 0;
    X[0] = x;
    Y[0] = y;
    FOR(i,0,N) {
      DRI(l);
      A[i] = l;
      switch(d) {
        case 0: y += l; break;
        case 1: x += l; break;
        case 2: y -= l; break;
        case 3: x -= l; break;
      }
      d++;
      d %= 4;
      X[i+1] = x;
      Y[i+1] = y;
    }
    lns.clear();
    mpx.clear();
    mpy.clear();
    sort(X,X+N+1);
    sort(Y,Y+N+1);
    cord c;
    FOR(i,0,N+1) {
      c.real = X[i];
      c.idx = i;
      mpx.insert(c);
    }
    FOR(i,0,N+1) {
      c.real = Y[i];
      c.idx = i;
      mpy.insert(c);
    }
    x = y = d = 0;
    line ln;
    FOR(i,0,N) {
      int l = A[i];
      switch(d) {
        case 0:
          ln.x1 = x;
          ln.x2 = x;
          ln.y1 = y+l;
          ln.y2 = y;
          break;
        case 1:
          ln.x1 = x;
          ln.x2 = x+l;
          ln.y1 = y;
          ln.y2 = y;
          ln.begin = true;
          lns.insert(ln);
          ln.begin = false;
          break;
        case 2:
          ln.x1 = x;
          ln.x2 = x;
          ln.y1 = y;
          ln.y2 = y-l;
          break;
        case 3:
          ln.x1 = x-l;
          ln.x2 = x;
          ln.y1 = y;
          ln.y2 = y;
          ln.begin = true;
          lns.insert(ln);
          ln.begin = false;
          break;
      }
      lns.insert(ln);
      switch(d) {
        case 0: y += l; break;
        case 1: x += l; break;
        case 2: y -= l; break;
        case 3: x -= l; break;
      }
      d++;
    }
    for(set<line>::iterator it = lns.begin(); it != lns.end(); ++it) {
      cout << "line" << endl;
      line ln = *it;
      if(ln.hor()) {
        // check diff od abs?
        if(ln.begin) {
          update(ln.y1,-1); // higher
          update(ln.y2,1);
        } else {
          update(ln.y1,1);
          update(ln.y2,-1);
        }
      } else {
        // vertical
        // test
        if(read(ln.y1) > read(ln.y2)) {
          // TODO intersect
          cout << "intersect" << endl;
        }
      }
    }
    */
  //}