first subtract from the maximum number in the N-bit system, that is 2N-1 (this term in binary is actually a simple number consisting of 'all 1s', and a subtraction from it can be done simply by inverting all bits in the number also known as the bitwise NOT operation) and then adding the one. Coincidentally, that intermediate number before adding the one is also used in computer science as another method of signed number representation and is called a Ones' complement (named that because summing such a number with the original gives the 'all 1s').