#include <bits/stdc++.h>

using namespace std;

int main(){
    string s;
    cin >> s;
    int cnt = 0;
    for(int i=0;i<s.size();i++){
        cnt += s[i] - '0';
    }
    cnt %= 9;
    if (cnt == 0){
        cout << 9 << endl;
    } else {
        cout << cnt << endl;
    }
}