How can I use NaN on my if statement as a condition on java

I wanna use NaN on my if statement, so every time that area == NaN, it shows up a System.out.println message, on java. How do I do it?

if (met.area == NaN){
    System.out.println("Input is invalid. PLease input a valid triangle");
  }
  else{
  System.out.println("Triangle area is : " + met.area);
  }