project euler之甚至斐波那契数字（Even Fibonacci numbers）

    fib = [1,2]
    i = 0
    while fib[-1] < 4000000:
        fib.append(fib[i]+fib[i+1])
        i += 1
    sums = 0
    for n in fib:
        if n % 2 == 0:
            sums += n
    print(sums)