#include <iostream>
#include <vector>
using namespace std;

vector<int> pref_sum;
int n;
int suma(int i, int j) {
    if(j < 0 or j >= n) {
        return 0;
    }
    if(i - 1 < 0) {
        return pref_sum[j];
    }
    return pref_sum[j] - pref_sum[i - 1];
}
int main() {
    cin >> n;
    int niza[n];
    for(int i = 0; i < n; i++) {
        cin >> niza[i];
    }
    int sum = 0;
    for(int i = 0; i < n; i++) {
        sum += niza[i];
        pref_sum.push_back(sum);
    }
    for(int i = 0; i < n; i++) {
        int S = 0;
        int E = i - 1;
        int sum_left = suma(S, E);

        S = i + 1;
        E = n - 1;
        int sum_right = suma(S, E);

        if(sum_left == sum_right) {
            cout << i + 1 << endl;
            return 0;
        }

    }
    cout << -1 << endl;
    return 0;
}