#include <iostream>
#define int long long 

using namespace std;

const int MAX_N = 1e5;
int a[MAX_N + 1];
int n;

signed main() {
	cin >> n;
	int s = 0;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
		s += a[i];
	}
	for (int i = 1; i <= n; i++) {
		if ((s - a[i]) + -a[i] == 0) {
			cout << i;
			return 0;
		}
	}
	cout << "-1";
	return 0;
}