3 of 6 -s, not -v

><>, 46 43 + 4 for  -s= = 47 bytes

0&l?!v:f4*=?\l&:@+n$o!
00.  >&n;   >&:n1+$o

This is an implementation of xnor's algorithm in ><>.

It takes the input string on the stack (-s flag with the standard interpreter).

You can try it out on the online interpreter.