Fast Fibonacci algorithm

fibonacci.py

def fibonacci(n):
    if n <= 2:
        return 1
    elif n <= 0:
        return 0

    if n % 2 == 0:
        x = n/2
        return fibonacci(x) * (fibonacci(x + 1) + fibonacci(x - 1))
    else:
        x = (n-1)/2
        return fibonacci(x+1)**2 + fibonacci(x)**2

if __name__ == "__main__":
    while True:
        print "Enter number:"
        input = int(raw_input())
        if input < 0:
            break
        print "Processing..."
        print "Result: " + str(fibonacci(input))