#include <iostream>
using namespace std;

int main(){
    int n;
    cin >> n;
    for(int i = 0; i < 100; i++){
        int old = n;
        n = 0;
        while(old > 0){
            n += old%10;
            old /= 10;
        }
    }
    cout << n << endl;
    return 0;
}