Break the code

6 5 2 3 X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X
X X X X

How to Play.
The code is a 4 digit number containing the digits 1 to 6 No digit is repeated in the code.
Tap the digits in the lower grid to make your guess and tap Go to score. Tap DEL to delete the last digit entered.
The tile to the right shows a green square for each correct digit in the right place, and a yellow square for each correct digit in the wrong place.