import argparse

def main(args):
    n = 0
    d = 1
    p = 2

    for i in range(args.iterations):
        if i%2:
            d += 2
        else:
            n += 2

        p *= (n/d)

        if args.verbose:
            print("%d: %f" % (i+1,p))

    print(p)

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Calculate pi using the Wallis product formula.')
    parser.add_argument('iterations', nargs='?', default=1000000, type=int,  help='Number of terms in the product')
    parser.add_argument('-v', '--verbose', dest='verbose', action='store_true',  help='Show the result of each iteration (warning: huge performance penalty)')
    args = parser.parse_args()
    main(args)