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 <stdio.h>

int main(){
  int x,y,tmp,i,res;

  scanf("%d %d", &x, &y);
  if(y>x){ // x>=y にする
    tmp=x;
    x=y;
    y=tmp;
  }
  x= x%y;
  res= y;
  //x(x&y)とyの最大公約数を求める
  for(i=x; i>0; i--) if(x%i==0 && y%i==0){
      res=i;
      break;
    }
  printf("%d\n", res);

  return 0;
}