Euler #50

def prime(n):
    if n == 2 or n == 3: return True
    if n < 2 or n % 2 == 0: return False
    if n < 9: return True
    if n % 3 == 0: return False
    r = int(n**0.5)
    f = 5
    while f <= r:
        if n % f == 0: return False
        if n % (f+2) == 0: return False
        f += 6
    return True

total, chain, bestchain, index, primes, bestprime = 0, 0, 0, 0, [], 0
for x in range(10**6):
    print(x)
    if prime(x):
        primes.append(x)
        if (total + x) >= 10**6:
            if (total + x) >= 10 ** 6:
                total -= primes[index]
                index += 1
                chain -= 1
                continue
        total += x
        chain += 1
    if prime(total) and (total < 10**6):
        if chain > bestchain:
            bestchain = chain
            bestprime = total
print(bestprime)