Vitsy, 13 12 Bytes

Byte size reduced by newest version ending execution on end of file*.

I\[i1+2M]l\N;
I\             Repeat everything in the [] for input stack's length.
  [i1+2M]      Grab an item from the input, add 1 and modulo 2 (to invert the number).
         l\    Repeat the next character for the currently active program stack's length.
           N   Output the top item of the stack as a number.

*In situations that don't involve special cases.

Vitsy, 13 12 Bytes

Byte size reduced by newest version ending execution on end of file*.

I\[i1+2M]l\N
I\             Repeat everything in the [] for input stack's length.
  [i1+2M]      Grab an item from the input, add 1 and modulo 2 (to invert the number).
         l\    Repeat the next character for the currently active program stack's length.
           N   Output the top item of the stack as a number.

*In situations that don't involve special cases.

Vitsy, 13 Bytes

I\[i1+2M]l\N;
I\             Repeat everything in the [] for input stack's length.
  [i1+2M]      Grab an item from the input, add 1 and modulo 2 (to invert the number).
         l\    Repeat the next character for the currently active program stack's length.
           N   Output the top item of the stack as a number.
            ;  End execution.

Vitsy, 13 12 Bytes

Byte size reduced by newest version ending execution on end of file*.

I\[i1+2M]l\N;
I\             Repeat everything in the [] for input stack's length.
  [i1+2M]      Grab an item from the input, add 1 and modulo 2 (to invert the number).
         l\    Repeat the next character for the currently active program stack's length.
           N   Output the top item of the stack as a number.

*In situations that don't involve special cases.

Vitsy, 8 Bytes

I\irl\O;
I\       Repeat the next character for input stack's length.
  i      Grab an item from the input.
   r     Reverse the current stack.
    l\   Repeat the next character for the currently active program stack's length.
      O  Output the top item of the stack as a character.
       ; End execution.

Vitsy, 13 Bytes

I\[i1+2M]l\N;
I\             Repeat everything in the [] for input stack's length.
  [i1+2M]      Grab an item from the input, add 1 and modulo 2 (to invert the number).
         l\    Repeat the next character for the currently active program stack's length.
           N   Output the top item of the stack as a number.
            ;  End execution.