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

dp=[0]*n
dp[0]=A[0]
if n==1:
    exit(print(A[-1]))
dp[1]=max(A[0],A[1])
if n==2:
    print(dp[-1])
    exit()

for i in range(1,n):
    dp[i]=max(dp[i-1],dp[i-2]+A[i])

print(dp[-1])