#include <stdio.h>

int main()
{
	int N;

	if (scanf("%d", &N) != 1) {
		return -1;
	}

	for (int i = 1; i <= 100; i++) {
		int tmp = 0;
		while (N != 0) {
			tmp += N % 10;
			N = (N - (N % 10)) / 10;
		}
		N = tmp;
	}

	printf("%d", N);

	return 0;
}