#include <stdio.h>
#include <stdlib.h>

struct Number{
    int value;
    
};

int sumOfDigits(struct Number num) {
    
    int n = abs(num.value);
    int sum = 0;
    
    while ( n > 0 ) {
        sum += n%10;
        n /= 10;
    }
    
    return sum;
    
}

int main(){
    int n;
    scanf("%d", &n):
    
    if ( n < 0 ) {
        printf("Invalid input"):
        return 0;
    }
    
    struct Number num;
    num.value = n;
    
    int result = sumOfDigits(num);
    printf("%d", result);
    
    return 0;
}