#include <stdio.h>

int main() {

int month;

printf("input month : ");

scanf("%d", &month);

if (month < 1 || month > 12) {

puts("Error");

return 0;

}

switch (month) {

case 1:

case 3:

case 5:

case 7:

case 8:

case 10:

case 12:

puts("31");

break;

case 4:

case 6:

case 9:

case 11:

puts("30");

break;

case 2:

puts("28 or 29");

break;

default:

puts("Error");

}

return 0;

}