N = int(input()) Vs = list(map(int, input().split())) def solve(N, Vs): if N == 1: return Vs[0] dp = [0] * N dp[0] = Vs[0] dp[1] = max(Vs[0], Vs[1]) for i, v in enumerate(Vs[2:], 2): dp[i] = max(dp[i-1], dp[i-2] + v) return dp[-1] print(solve(N, Vs))