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

dp=[[0]*2 for n in range(N+1)]

for n in range(N):
	v=v_list[n]
	dp[n+1][0]=max(dp[n][0],dp[n][1])
	dp[n+1][1]=dp[n][0]+v 
	
print(max(dp[N]))