What is the minimum number of NAND gates needed to implement the below given Boolean expression?
F(A, B, C, D) = A̅.B̅.C̅.D + A̅.B̅.C.D̅ + A̅.B̅.C.D + A̅.B.C̅.D + A̅.B.C.D̅ + A̅.B.C.D + A.B̅.C̅.D + A.B̅.C.D̅ + A.B̅.C.DEnter numerical value using the virtual keypad. Round off where necessary.