N = int(input())
V = list(map(int,input().split()))
pick = [0] * (N + 1)
pick[0] = 0
pick[1] = V[0]
if (N >= 2):
  for i in range(2,N+1):
    pick[i] = max(pick[i-1],pick[i-2] + V[i-1])
else:
  pass
    
print(pick[N])