#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define itn int
#define rep2(i,a,n) for(int i = (a);i < (n);i++)
#define rep(i,n) rep2(i,0,n)
using P = pair<int,int>;

int main(void){
    string s;
    cin >> s;
    
    int ans = 0;
    for(int i = 0;i < s.size();i++){
        ans += s[i]-'0';
    }
    cout << ans << endl;
    
}