h.py

a = [1,2,16,19,18,0]

i = [-1] * 30000001
for x,y in enumerate(a): i[y]=x

l = 0
x = len(a) + 1

while x < 30000000:
	k = l
	if i[l] > -1:
		l = x - i[l] - 1
	else:
		l = 0
	i[k] = x - 1
	x += 1

print(l)