#include <stdio.h>
 struct Number{
     int n;
     int sum;
 };
 void calulatedSum(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(&num);
     printf("%d",num.sum);
     return 0;
 }