N = int(input())
V = list(map(int,input().split()))
dp = [[0] * 2 for _ in range(N+1)]

for i in range(N):
  # vを取らないとき
  dp[i+1][0] = max(dp[i+1][0], dp[i][0], dp[i][1])

  # vをとったとき
  dp[i+1][1] = max(dp[i+1][1], dp[i][0] + V[i])

print(max(dp[N]))