#include<stdio.h>
struct Number{
    int n;
};
int sumdigits(struct Number num){
    int sum=0;
    int temp=num.n;
    while(temp>0){
        sum+=temp%10;
        temp/=10;
   }
   return sum;
}
int main(){
    struct Number num;
    scanf("%d", &num.n);
    if(num.n<0){
        printf("Invalid input")
    }else{
        int result=sumdigits(num);
        printf("%d", result);
    }
    return 0;
}