#include <stdio.h>
#include <utility>
#include <algorithm>


using namespace std;

int seq[12345];
int main(void){
	int n;
	while(scanf("%d", &n) == 1){
		for(int i = 0; i < n; i++){
			scanf("%d", &seq[i]);
		}
		if(n==1){
			printf("1\n");
		}
		else{
			int d = seq[n-1] - seq[n-2];
			int i = n-1;
			//printf("%d D\n", d);
			while(i > 0 && seq[i] - seq[i-1] == d){
				i--;
			}
			printf("%d\n", i+1);
		}
	}
	return 0;
}