#include <stdio.h>

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

    for (i = 0; i < 20; i++)
        printf("gcd of 12 and %d is %d\n", i, gcd(12, i));
    return 0;
}

int gcd(int a, int b)
{
    while (a) {
        int t = b;
        b = a;
        a = t % a;
    }
    return b;
}