Problem: the unit digit in the product 4556 * 3432 * 4581 * 2784 is ?
Rationale: unit digit in the given product = unit digit in 6 * 2 * 1 * 4 = 8 answer is a
annotated_formula: subtract(multiply(multiply(multiply(4556, 3432), 4581), 2784), subtract(multiply(multiply(multiply(4556, 3432), 4581), 2784), add(const_4, const_4)))