#include <iostream>

using namespace std;


int main()
{

int n = 0;

while (cin >> n) {

int v = 0;
int vv = 0;
int idx = 0;
int diff = -1;

for (int j=0; j<n; ++j) {

cin >> v;

if (j>1) {
  
  if (diff != v - vv) {
  	idx = j-1;
  }
 
  diff = v - vv;
  vv = v;

  //cout << "v:" << v << " i:" << idx << " "<< diff << " ";
  
} else {
  idx = 0;
  diff = v - vv;
  vv = v;
  //cout << "v:" << v << " i:" << idx << " "<< diff << " ";
}

}

cout << idx +1 << endl;
}


return 0;
}