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

N, = map(int, raw_input().split())
V = map(int, raw_input().split())

# 動的計画法
maxv = {len(V)+1: 0}
for i in xrange(len(V), -1, -1):
    if i >= len(V):
        maxv[i] = 0
    else:
        maxv[i] = max(V[i] + maxv[i + 2], maxv[i + 1])

print maxv[0]