#include <stdio.h>

int main() {
    int n,  sum = 0, temp;
    scanf("%d", &n); 
    if (n < 0) {
        print f("invalid input");
        
    } else {
        temp = n;
        while (temp > 0) {
            sum += temp % 10;
            temp /= 10;
        }
        printf ("%d", sum);
        
    }
    return 0;
}