#include<stdio.h>

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