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

dp=[[0 for i in range(2)] for j in range(N+1)]
ans = 0
for i in range(N):
   dp[i+1][0] = max(dp[i][1],dp[i][0])
   dp[i+1][1] = dp[i][0]+V[i]
   ans = max(ans,dp[i+1][0])
   ans = max(ans,dp[i+1][1])
print ans