C B A->Y
0 0 0 Y=1
1 0 0 Y=1
1 1 0 Y=0
0 1 0 Y=0
0 1 1 Y=0
1 1 1 Y=0
1 0 1 Y=0
0 0 1 Y=1
function: Y = (!C && !B && !A || C && !B && !A || !C && !B && A)