def factorial(n):
    if n == 0:
        return 1
    else:
        return n * factorial(n-1)


def permutations(r, n):
    return factorial(n)/factorial(n-r)

def combinations(k, n):
    return factorial(n)/(factorial(k)*factorial(n-k))

def main():

    GRID_SIZE = 20

    # v1 = (0,1)
    # v2 = (1,0)

    # all possible combinations of a set containing:
    # GRID_SIZE of v1 and GRID_SIZE of v2

    # doesn't matter what the vectors themselves are tho.

    TYPES_OF_VECTORS = 2
    NUM_VECTORS = TYPES_OF_VECTORS * GRID_SIZE

    print permutations(NUM_VECTORS, NUM_VECTORS)/factorial(GRID_SIZE)**TYPES_OF_VECTORS

if __name__ == '__main__':
    main()