#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("enter an integer:");
    if(scanf("%d",&input_num.value)!=1){
        printf("invalid input\n");
        return 1;
}
if(input_num.value<0){
    printf("invalid input\n");
    return 1;
}
int result=sum_of_digits(input_num);
printf("the sum of the digits is:%d\n",result);
return 0;
}