def macmahon(a , b , c):
    """
    Returns MacMohan formula for the number M(a,b,c).
    It is equal to the number of plane partitions that fit in an (a×b×c) box.

    Parameters
    ----------
    a : int
        denotes length of box
    b : int
        denotes breadth of box
    c : int
        denotes height of box
    return  : int
        returns value of MacMohan formula

    """
    if(a!=int(a) or b!=int(b) or c!=int(c)):
        raise ValueError(
            "dimnsions must be positive integer"
        )
    ans = 1
    for i in range(1,a+1):
        for j in range(1,b+1):
            for k in range(1,c+1):
                ans *= (i+j+k-1)/(i+j+k-2)
    return ans