import time

def lucas(n):
    """Calculates recursively the n-th lucas number.
       The function assumes that its input is a non-negative
       integer, otherwise it will run indefinitely long."""
    
    if n==0:
        return 2
    if n==1:
        return 1
    return lucas(n-1)+lucas(n-2)

def timeit(func):
    for n in range(100):
        start = time.time()
        value = func(n)
        duration = time.time()-start
        print(n, value, duration)
        if duration > 0.5:
            break