Ocaml - Same Random.int

I have a problem with the module Random.int in Ocaml.

So I have a program with for example :

let a : int = Random.int 100;;
-> val a : int = 44

The problem is that when I launch the program with emacs and I run it with ctrl-c ctrl-b, I have every time the same result.

I have already test to put Random.self_init or Random.full_init in the top of the program but it's also the same result.

Thanx for helping me