#include <stdio.h>

int main() {
    int n;
     scanf("%d", &n);
     int sum = 0;
     while(n / 10) {
        while(n) {
            sum += n % 10;
            n /= 10;
        }
            n = sum;
            sum = 0;

     }
     printf("%d", n);
    return 0;
}