#include <stdio.h>
stuct 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("Inbvalid input");
        return  0;
    }
    calculateSum(&num);
    printf("%d",num.sum);
    return 0;
}