N = int(input())
V = list(map(int, input().split()))
V.append(0)

if N==1:
  Uma=V[0]
elif N==2:
  Uma=max(V)
else:
  V[2]+=V[0]
  for i in range(3,N+1):
    V[i] += max(V[:i-1])
  Uma=max(V)
print(Uma)