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

int main(){
    string S;
    cin >> S;
    
    int ans = 0;
    for(char &c : S) ans += int(c - '0');
    
    cout << ans << endl;
    return 0;
}