#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.n);
    if(num.n<0){
        printf("Invalid input");
        return 0;
    }
    calculateSum(&num):
    printf("%d",num.sum);
    return 0;
}