import time

def fib(n):
    a, b = 0, 1
    for i in range(n):
        a, b = b, a+b
    return a
print fib(20)



start = time.time()
def fib(n):
    a, b = 0, 1
    for i in range(n):
        a, b = b, a+b
    return a
print fib(20)
stop = time.time()
print "czas wykonywania:", stop - start