awk if/else conditions and printing last line

My two example files looks like this:

F1

Red -
Blue -
Green -

F2

Yellow +
Pink +
ColorX +

I need awk script to print first/last line depending on $2 Field (If $2 == "+" -- print first line; else -- print last line).

I managed to write awk script that prints first line, but how can I add else in order to print last line?

awk '{if (NR == 1 && $2 == "+") print}' F2
Yellow +

How can I modify this code to input F1 and get Green - printed?

Maybe it is possible to add something like this: awk '{if (NR == 1 && $2 == "+") print ; else {END print} }'

Answer

awk 'NR == 1 && $2 == "+" { print ; p=1 ; exit } 
     END { if (p != 1) { print $0 } }' INPUTFILE

Note: this assumes, that if the first line does not contains '+' the last line must get printed.