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

if N == 1:
    print(V[0])
    exit()
elif N == 2:
    print(max(V[0],V[1]))
    exit()

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