/*
 * twin.c - find the first two twin prime pairs greater than 1000.
 *
 * Algorithm: Start with 1001, go up by twos; for each prime number, check
 * isprime(i+2).
 */

#include <stdio.h>

int main()
{
    int i, nleft;
    extern int isprime(int p);

    nleft = 2;
    for (i = 1001; nleft > 0; i += 2) {
	if (isprime(i) && isprime(i+2)) {
	    printf("%d %d\n", i, i + 2);
	    nleft = nleft - 1;
	}
	/*
	 * we needn't worry that in the next loop iteration, we'll print an
	 * overlapping twin prime... because that would constitute a triplet
	 * and the only one of these is 3,5,7, which is <1000.
	 */
    }

    return 0;
}