public class Sdddd {

 int month = new scanner(System.in);
{
  if (month == 1)
 System.out.println("31");
else if (month == 2)
  System.out.println("28");
 else if (month == 3)
  System.out.println("30");
 else if (month == 4)
  System.out.println("31");
 else if (month == 5)
  System.out.println("30");
 else if (month == 6)
  System.out.println("31");
 else if (month == 7)
  System.out.println("30");
 else if (month == 8)
  System.out.println("31");
 else if (month == 9)
  System.out.println("30");
 else if (month == 10)
  System.out.println("31");
 else if (month == 11)
  System.out.println("30");
 else if (month == 12)
  System.out.println("31");

}
}

두번째 줄이 문제인거같은데 뭔지 모르겠다.