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: Time Limit Exceeded)

#include <stdio.h>
#include <stdlib.h>

int main(){
  int a,b,i;

  scanf("%d%d",&a,&b);
  if (a<1||b<1||a>1000000000||b>1000000000) {
    printf("atai yokunai\n");
    exit(1);
  }
  if (a<b){
    i=a;
    a=b;
    b=i;
  }
  for (i=b;i>0;i--){
    if(b%i==0&&(a%b)%i==0){
      printf("%d\n",i);
      break;
    }
  }

  return 0;
}