# -*- coding: utf-8 -*-

import sys

n = int(raw_input().split()[0])
a1 = [int(i) for i in raw_input().split()]
a2 = [int(i) for i in raw_input().split()]

maxS = 0
for i in range(1, n + 2):
    s = sum(a1[:i]) + sum(a2[i - 1:])
    # print i, a1[:i], a2[i - 1:],
    if s > maxS:
        # print '!!',
        maxS = s
    # print
    
sys.stdout.write('%d\n' % maxS)
sys.stdout.flush()
