#include <bits/stdc++.h>

using namespace std;

int main() {
    int x;
    cin >> x;
    while (x >= 10) {
        int ans = 0;
        while (x > 0) {
            ans += x % 10;
            x /= 10;
        }
        x = ans;
    }
    cout << x << '\n';
}