N = int(input())
V = list(map(int,input().split()))
#dp[i][0]:V_iをとらない
#dp[i][1]:V_iをとる
dp = [[0 for __ in range(2)] for _ in range(N)]
dp[0][0] = 0
dp[0][1] = V[0]
dp[1][0] = V[0]
dp[1][1] = V[1]
for i in range(2,N):
    dp[i][0] = max(dp[i-1][1],dp[i-2][1])
    dp[i][1] = max(dp[i-2][1]+V[i],dp[i-1][0]+V[i])
print(max(dp[N-1][0],dp[N-1][1]))