#include <stdio.h>

int main()
{
	int i, N, M;
	scanf("%d", &N);
	for (i = 2; i <= 100; i++) {
		for (M = 0; N > 0; M += N % 10, N /= 10);
		N = M;
	}
	printf("%d\n", N);
	fflush(stdout);
	return 0;
}