#include <stdio.h>
 
#define COG1_TEETH    4
#define COG2_TEETH    25
#define COG3_TEETH    4
#define BASE          1584
/* BASE == (4 * COG1_TEETH * COG2_TEETH * COG3_TEETH - 16) */
  
int isleap(int year);
 
int main(void)
{
    int year;

	for (year = 1994; year < 2101; year++) {
		printf("%d is %s\n", year,
                isleap(year) ? "a leap year" : "not a leap year");
	}
    
    return 0;
}
  
int isleap(int year)
{
    unsigned a, b, c;
    unsigned i;
         
    if (year < BASE) return 0;      /* Not Gregorian year */
     
    a = 0;
    b = COG2_TEETH - COG1_TEETH;
    c = COG3_TEETH - 1;
    i = year - BASE;
     
    while (i--) {
        if (++a == COG1_TEETH) {
            a = 0;
            if (++b == COG2_TEETH) {
                b = 0;
                if (++c == COG3_TEETH)
                    c = 0;
            }
        }
    }
  
    return !b ? !a && !c : a == 0;
}