#int(input())
#map(int, input().split())
#list(map(int, input().split()))

N = int(input())
V = list(map(int, input().split()))

dp = [0, 0]

for i in range(N):
    ndp = [0, 0]
    ndp[0] = max(dp)
    ndp[1] = dp[0] + V[i]
    dp = list(ndp)

print(max(dp))