#include<stdio.h>
struct Number
{
    int value
};
int sum_of_digits(struct Number num)
{
    int sum=0;
    int n = num.value;
    if(n==0)
    {
        return 0;
    }
    while(n!=0)
    {
        sum += n%10;
        n/=10;
    }
    return sum;
}
int main()
{
    struct Number input_num;
    printf("invalid input");
    if(scanf("%d",&input_num.value)!=1)
    {
        printf("invalid output");
        return 1;
    }
    if(input_num.value<0)
    {
        printf("invalid input");
        return 1;
    }
    int result = sum_of_digits(input_num);
    printf("the sum of digits is:",result);
    return 0;
}