#include <iostream>
using namespace std;

int digit(int x) {
	int ret = 0;
	while(x > 0) {
		ret += x % 10;
		x /= 10;
	}
	return ret;
}

int main() {
	int n;
	cin >> n;
	for (int i = 1; i < 100; i++) {
		n = digit(n);
	}
	cout << n << endl;
	return 0;
}