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

dp = [[0,0] for _ in range(n+2)]
for i in range(n):
  if i+1 < n:
    dp[i+2][1] = dp[i][0] + V[i+1]
  dp[i+1][1] = max(dp[i+1][1], dp[i][0] + V[i])
  dp[i+1][0] = max(dp[i+1][0], dp[i][1]) 

print(max(dp[n]))