#include <stdio.h>

struct Number {
    int value;
};

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