#include <bits/stdc++.h>
using namespace std;
template <typename T> using vec = vector<T>;
template <typename T> using vvec = vector<vector<T>>;

int main() {
    int n; cin >> n;

    for (int i = 0; i < 100; ++i) {
        int sum = 0;
        while (n) {
            sum += n % 10;
            n /= 10;
        }
        n = sum;
    }

    cout << n << endl;
}