#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; ++i)
typedef long long ll;
using namespace std;

int main() {
    cin.tie(0)->sync_with_stdio(0);

    string S;
    cin >> S;

    int ans = 0;
    for (char c : S) {
        ans += (c - '0');
    }
    cout << ans << "\n";

    return 0;
}