http://uva.onlinejudge.org/external/113/11332.html

bpe10473_online.cpp

#include <iostream>;
#include <cstdlib>;
using namespace std;

int f(int n)
{
	int sum = 0;
	while (n)
	{
		sum += n%10;
		n = n/10;
	}
	
	return sum;
}

int g(int n)
{
	int r = f(n);
	if (1 <= r && r <= 9) return r;
	else return g(r);	
}

int main(void)
{
	int n;
	while (cin >> n)
	{
		if (n == 0) break;
		else cout << g(n) << endl;
	}
	return 0;
}