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

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

print(max(dp[n]))