S1 | S0 | I0 | I1 | I2 | I3 || Out
----------------------------------
 0 |  0 |  X |  X |  X |  X ||  I0
 0 |  1 |  X |  X |  X |  X ||  I1
 1 |  0 |  X |  X |  X |  X ||  I2
 1 |  1 |  X |  X |  X |  X ||  I3

S1 | S0 | I0 | I1 | I2 | I3 || Out
----------------------------------
 0 |  0 |  1 |  0 |  0 |  1 ||  1
 0 |  1 |  1 |  0 |  0 |  1 ||  0
 1 |  0 |  1 |  0 |  0 |  1 ||  0
 1 |  1 |  1 |  0 |  0 |  1 ||  1

S1 | S0 || Out
--------------
 0 |  0 ||  1
 0 |  1 ||  0
 1 |  0 ||  0
 1 |  1 ||  1