Incrementing one time in fixed update

Hello!
I want my character jumps higher and higher after each of his jumps.

His jumps are based on physics, so I use a Fixed Update for make him jump. But i want my script to increment one time a value after that the avatar has jumped.

It’s possible to incrementing just one time in fixed update? If yes, how i do?

there is the script I use in the fixedupdate to make my avatar jump (and the value numberjump is the one i want to increment one time by jump):

		if ((canjump == true) && (Input.GetButton ("Jump"))) 
		{
			Vector3 up = new Vector3 (0.0f, upper, 0.0f); // script for jumping
			rb.AddForce (up * upper);
			numberjump++;
		}

Try using:

Input.GetButtonDown("Jump")

instead!