There's a big gate that gets opened by stepping on a pressure plate. There are 4 plates total, 2 on each side of the big gate. The gate is opened when any (or both) plates are stepped on. Find the simplified boolean function to make this work.

So my input/output look somewhat like this. (Assume S1,S2 is inside and S3,S4 is outside)

S1 S2 S3 S4 | F

0 0 0 0 0

0 0 0 1 1

0 0 1 0 1

0 0 1 1 1

0 1 0 0 1

0 1 0 1 1

0 1 1 0 1

0 1 1 1 1

1 0 0 0 1

1 0 0 1 1

1 0 1 0 1

1 0 1 1 1

1 1 0 0 1

1 1 0 1 1

1 1 1 0 1

1 1 1 1 1

Then, there's a problem. There's few cases where some inputs are an impossibility. For instance, you cannot step on the outside plate and inside plate at the same time or step on more than 2 plates at the same time so this eliminates many possible inputs (Such as 1,1,1,1 or 1,0,0,1). How do I eliminate this condition to simplify my equation as much as possible when drawing my K-map?