#include <iostream>
using namespace std;

int f(int n) {
    int s = 0;
    int nn = n;
    while (n) {
        s += n%10;
        n /= 10;
    }
    if (nn == s)
        return s;
    return f(s);
}

int main() {
    int n;
    cin >> n;
    cout << f(n);
}