#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
int main() {
// ifstream inp;
// ofstream otp;
// inp.open("input.txt");
// otp.open("output.txt");
auto &inp = cin;
auto &otp = cout;
double k = 0, n = 0, s1 = 0, s2 = 0;
vector<int> a(1000000);
inp >> n;
for (int i = 0; i < n; i++) {
inp >> a[i];
}
// Считаем частичные суммы
vector<int> s(1000000);
s[0] = a[0];
for (int i = 1; i < n; i++) {
s[i] = s[i-1] + a[i];
}
for (; k <= n; k++) {
s1 = 0;
s2 = 0;
if (k == n) {
otp << "-1";
break;
}
else {
// for (int i = 0; i < k; i++) {
// s1 += (int)a[i];
// }
// for (int i = k; i < n; i++) {
// s2 += (int)a[i];
// }
// Используем частичные суммы вместо прямого подсчета сумм
s1 = s[k];
s2 = s[n-1] - s[k];
if (s1 == s2) {
otp << k + 1;
break;
}
}
}
return 0;
}
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