#include<stdio.h>
struct Number{
    int n;
    int sum;

};
void calculatedSum(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.n);
    if(num.n<0){
        printf("invalid input");
        return 0;
    }
    calculatedSum(&sum);
    printf("%d",num.sum);
    return 0;
}