题解 | #Digital Roots#

#include<iostream>

using namespace std;

int main()
{
	int n;
	while(cin >> n)
	{
		int x = n;
		while(x / 10 != 0)
		{
			int t = x, sum = 0;
			while(t != 0) {
				sum += t % 10;
				t /= 10;
			}
			x = sum;
		}
		cout << x << endl;
	}
	return 0;
}