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

DP=[0 for i in range(N+1)]
DP[1]=V[0]

for i in range(1,N):
    max_num=max(DP[i-2 if i-2>0 else 0:i])
    DP[i+1]=max([max_num+V[i],max_num])
print(max(DP[N-1 if N-1>0 else 0:N+1]))