Stepik_Task_13

//goo.gl/RGA6EX
#include <iostream>
#include <cmath>
using namespace std;

int sum() {
    int n;
    cin >> n;
    if (n == 0) {
        return n;
    }
    return n + sum();
}

int main() {
    cout << sum();
    return 0;
}