#include <stdio.h>

#define BASE 10

int numberroot(int n)
{
    int temp;

    while(n >= BASE) {
        temp = n;

        n = 0;
        while(temp) {
            n += temp % BASE;
            temp /= BASE;
        }
    }

    return n;
}

int main(void)
{
    int n;

    scanf("%d", &n);

    printf("%d\n", numberroot(n));

    return 0;
}
/**************************************************************
	Problem: 1514
	User: admin
	Language: C
	Result: Accepted
	Time:12 ms
	Memory:1144 kb
****************************************************************/