#include <bits/stdc++.h>
#define REP(A,B) for(int (A)=0;(A)<(B);(A)++)
using namespace std;
int A[1111];
int main()
{
	int n;
	while(scanf("%d", &n) == 1) {
		REP(i, n) scanf("%d", A+i);
		int c = n-1;
		if(n == 1) printf("%d\n", 1);
		else {
			int d = A[n-2]-A[n-1];
			int last = A[n-2];
			int j = n-2;
			while(j-1 >= 0 && A[j-1] == last+d) {
				last = A[j-1];
				j--;
			}
			
			printf("%d\n", j+1);
		}
	}
	return 0;
}