Problem:
Greatest Common Divisor

Write a program which finds the greatest common divisor of two natural numbers a and b

Input

a and b are given in a line sparated by a single space.

Output

Output the greatest common divisor of a and b.

Constrants

1 ≤ a, b ≤ 109

Hint

You can use the following observation:

For integers x and y, if x ≥ y, then gcd(x, y) = gcd(y, x%y)

Sample Input 1

54 20

Sample Output 1

2

Sample Input 2

147 105

Sample Output 2

21

Solution in C++ (judge verdict: Accepted)

#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < (n); i++)

using namespace std;

const int inf = 1e9 + 7;

int main() {
	long long int x,y;
	cin >> x >> y;
	long long int d = max(x,y)%min(x,y);
	long long int ans = min(d,min(x,y));
	long long int tmp = min(x,y);
	if(x == y){
		cout << x << endl;
		return 0;
	}
	while(ans > 0){
		if(d%ans == 0 && tmp%ans == 0){
			cout << ans << endl;
			return 0;
		}
		ans--;
	}
	return 0;
}