32
In decimal system: $...-3, -2, -1, 0, 1, 2, 3...$
In binary system: $...-11, -10, -1, 0, 1, 10, 11...$
In unary system: $-111, -11, -1, \text{ ??? }, 1, 11, 111...$
I only found a related question but with no answers so far:
unary numbers: base-1 numeral system