#include <iostream>
using namespace std;

int Sum(int n)
{
	int sum = 0;
	while (n > 0)
	{
		int du = n % 10;
		sum += du;
		n = n / 10;
	}
	return sum;
}
void main()
{
	int n;
	do {
		cout << "Nhap 1 so nguyen:";
		cin >> n;
	} while (n < 0);
	cout << "Sum = " << Sum(n);
}