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>
int main()
{
    int i,j,n;
    do
    {
        int G=0;
        scanf("%d",&n);
        if (n==0)
        {
            break;
        }
        else
        {
            for(i=1;i<n;i++)
            {
                for(j=i+1;j<=n;j++)
                    {
                        G+=GCD(i,j);
                    }
            }
        }
        printf("%d\n",G);
    }while(n!=0);
    return 0;
}
int GCD(int i, int j)
{
    if (j!=0)
    {
        return GCD(j,i%j);
    }
    else
    {
        return i;
    }
}