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

int main() {
    string s;
    cin >> s;

    int ans = 0;
    rep(i, 0, s.length()) ans += s[i] - '0';
    cout << ans << endl;
    return 0;
}