ABC081A - Placing Marbles

問題：A - Placing Marbles

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

#define REP(i, n) for (int i = 0; i < (n); ++i)

int main(void) {
    string s;
    int ans = 0;

    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> s;
    REP(i, s.length()) {
        if (s[i] == '1') {
            ans++;
        }
    }

    cout << ans << "\n";
    return 0;
}