# coding: utf-8
# Your code here!
import sys
read = sys.stdin.read
readline = sys.stdin.readline

#n = int(readline())
n, = map(int,readline().split())
*a, = map(int,readline().split())

dp0 = dp1 = 0
for i in a:
    dp0, dp1 = max(dp0,dp1),max(dp1,dp0+i)
print(max(dp0,dp1))