In chapter 3 of Robert Pickerings book "Foundations of F" I found the following example:

let mathsPuzzle() =

print_string "Enter day of the month which you were born: "

let input = read_int()

let x = input * 4 // Multiply it by 4

let x = x + 13

let x = x * 25

let x = x - 200

....

If I try to run it in the F# interactive console (F# 2.0 Interactive build 2.0.0.0) I get the following error:

print_string "Enter day of the month which you were born: "

---^^^^^^^^^^^^

stdin(40,4): error FS0039: The value or constructor 'print_string' is not defined

I can fix this with:

let print_string x = printf "%s" x

However then I get the similar error on the next line:

let input = read_int()

---------------^^^^^^^^

stdin(64,16): error FS0039: The value or constructor 'read_int' is not defined

Here I could not find a way to avoid the error.

What do I need to do to avoid these error messages?