#include <stdio.h>
main() { 
   int year, month, len;
   while(1){
       printf("Enter year & month: \n");
       scanf("%d%d",&year, &month);
       switch(month)
        {
            case 1:  len=31; break;
            case 3:  len=31; break;
            case 5:  len=31; break;
            case 7:  len=31; break;
            case 8:  len=31; break;
            case 10: len=31; break; 
            case 12: len=31; break;
            case 4:  len=30; break;
            case 6:  len=30; break;
            case 9:  len=30; break;
            case 11: len=30; break;
            case 2:  if(year%4==0 && year%100 != 0 || year%400 == 0)
                       len=29;
                     else
                       len=28;
                     break;
            default: printf("Input error \n");
                     len=0;
                     break;
        }
        if(len != 0)
          printf("The lenth of %d, %d is %d \n", year, month, len);
    }
}