#include <stdint.h>
#include <stdio.h>

int main()
{
  int N;
  while(scanf("%d", &N) != EOF) {
    int nums[2000];
    int i = 0;


    if(N <= 1) {
      printf("1\n");
      scanf("%d" , &N);
      continue;
    }

    while(N--)
      scanf("%d", &nums[i++]);

    i--;
    

    int diff = nums[i] - nums[i-1];



    while(i) {
      if(nums[i] - nums[i-1] != diff)
	break;
      i--;
    }
    printf("%d\n", i+1);


  }
  return 0;
}