#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
	ll n;
	ios::sync_with_stdio(0);
	while (cin >> n) {
		vector<ll> v(n);
		for (int i = 0; i < n; i++) 
			cin >> v[i];
		if (n <= 2) {
			puts("1");
			continue;
		}
		ll dif = v[n-2]-v[n-1];
		int i;
		for (i = n-2; i >= 1; i--) {
			int newdif = v[i-1]-v[i];
			if (newdif != dif) {
				break;
			}
		}
		cout << i+1 << endl;
	}
}