N = int(input())
V = list(map(int,input().split()))
dp = [0,0] # dp[0] 取らない最大、dp[1] 取る
for v in V:
    dp2 = [0,0]
    dp2[0] = max(dp)
    dp2[1] = dp[0] + v
    dp = dp2
print(max(dp))