#include <cstdio>
#include <stdlib.h>

int n, i;
long arr[1000];

int first() {
  for(i = 0; i < n; i++) {
    scanf(" %ld", arr + i);
    //printf("%ld ", arr[i]);
  }

  if (n == 1) {
    return 1;
  }

  long diff = arr[n - 1] - arr[n - 2];
  //printf("Diff: %ld\n", diff);
  for(i = n - 1; i > 0; i--) {
    //printf("%lu\n", arr[i] - arr[i-1]);
    if (arr[i] - arr[i-1] != diff) return i + 1;
  }

  return 1;
}

int main() {
  while(scanf(" %d", &n) == 1) {
    printf("%d\n", first());
  }
  
  return 0;
}