#include <stdio.h>

int main(void) {

    int n;
	int i;
	int a;
	int sum;
	
	scanf("%d", &n);
	a = n;
	for(i = 1;i <= 100;i++){
		sum = 0;
		n = a;
		while(n != 0){
			sum += n % 10;
			n /= 10;
		}
		a = sum;		
	}
	printf("%d\n", a);

	return 0;
}