#include <stdio.h>

struct Number {
    int n;
};
int main () {
    struct Number num;
    int sum = 0;
    
    scanf("%d", &num.n);
    
    if (num.n < 0) {
        printf("Invalid input");
        return 0;
    }
    while (num.n > 0) {
        sum += num % 10;
        num.n / = 10;
    }
    printf("%d", sum);
    return 0;
}