memoized = {}
X = {1,2}

def num_ways(n):
    if n == 0:
        return 1
    if n < 0:
        return 0
    if memoized.get(n, None):
        return memoized.get(n)
    ways = 0
    for i in X:
        ways += num_ways(n-i)
    memoized[n] = ways
    print(memoized)
    return memoized[n]

print(num_ways(4))