#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

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

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

    for (int i = 1; i < 100; i++) {
        n = f(n);
    }

    cout << n << endl;

    return 0;
}