#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;


// 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);
            W = A[i];
            H = H - H2;
            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;
}