N = int(input()) #お寿司の数
V = list(map(int,input().split())) #おいしさ
pick = [0] * (N + 1)
pick[1] = V[0]
if (N == 1):
  pass
else:
  for i in range(2,N+1):
    pick[i] = max(pick[i-1],pick[i-2] + V[i-1])
    
print(pick[N])