#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for (int i = (a); i <= (b); i++)
#define FORD(i,a,b) for (int i = (a); i >= (b); i--)
#define REP(i,b) for (int i = 0; i < (b); i++)

int a[1005];

int main() {
    int n;
    while (scanf("%d", &n) == 1) {
        REP(i, n) scanf("%d", &a[i]);
        if (n == 1) {
            printf("1\n");
            continue;
        }
        int d = a[n-1] - a[n-2];
        int i = n-2;
        while (i > 0 && a[i] - a[i - 1] == d) {
            i--;
        }
        printf("%d\n", i + 1);
    }
    return 0;
}