```js
const number = prompt("Enter your number");
const txt = "You result is : ";

switch (number) {
  case (number >= 80 && number <= 100):
    document.write(`${txt} A+`);
    break;
  case (number >= 70 && number <= 80):
    document.write(`${txt} A gread`);
    break;
  case (number >= 60 && number <= 70):
    document.write(`${txt} B gread`);
    break;
  case (number >= 50 && number <= 60):
    document.write(`${txt} C gread`);
    break;
  case (number >= 33 && number <= 50):
    document.write(`${txt} D gread`);
    break;
  case (number >= 0 && number <= 33):
    document.write(`${txt}  Field !`);
    break;
  case (number > 100 || number < 0):
    document.write(`It's not a valid number. Please input any valid number.`);
    break;
  default:
    document.write(`Not input any number. Please input any number .`);
    break;
}
```