Saving a variable between levels?

I’m trying to have an int (Levels_Unlocked) increase by one every time the scene loads. I tried to do this using playerprefs with no success.

void Start () {
		PlayerPrefs.GetInt ("Level Unlocked");

		Levels_Unlocked += 1;

		PlayerPrefs.SetInt ("Level Unlocked", Levels_Unlocked);
}

Typo:

Levels_Unlocked = PlayerPrefs.GetInt ("Level Unlocked");