#include <bits/stdc++.h>

using namespace std;

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

	int x = n;
	for (int i = 1; i < 100; i++) {
		int t = x, sum = 0;
		while (t > 0) {
			sum += t%10;
			t /= 10;
		}
		x = sum;
	}

	cout << x << endl;

	return 0;
}