#include <stdio.h>

int main()
{
    int age;
    char buf[50];

    while (1) {
	printf("How old are you?\n");
	if (fgets(buf, 50, stdin) == NULL)
	    exit(0);
	if (sscanf(buf, "%d", &age) == 0)
	    printf("That is not a valid age.\n");
	else if (age < 0)
	    printf("A negative age is impossible.\n");
	else if (age < 4)
	    printf("Unlikely.\n");
	else
	    break;
    }
    printf("Big deal, I'm %d\n", age + 3);

    return 0;
}