n = int(input())
vl = list(map(int, input().split()))
max_v = [vl[0]]
for i in range(1, n) :
  if i == 1 :
    max_v.append(max(vl[0], vl[1]))
  else :
    max_v.append(max(max_v[i-1], max_v[i-2]+vl[i]))
print(max_v[-1])