#include <bits/stdc++.h>
using namespace std;

int main(){
    int n;
    cin >> n;
    for (int i = 0; i < 99; i++){
        int m = 0;
        while (n > 0){
            m += n % 10;
            n /= 10;
        }
        n = m;
    }
    cout << n << endl;
}