#include<stdio.h>
struct Number
{
    int value;
};
int sumofDigits(struct Number num){
    int sum=0,n=num.value;
    while(n>0){
        sum+=n%10;
    }
    return sum;
}
int main()
{
    struct Number num;
    scanf("%d",&num.value);
    if(num.value<0){
        printf("invalid\n");
    }else{
        printf("%d\n",sumofDigits(num));
    }
    return 0;
}