N=io.read("n")
A={}
for i=1,2 do
  A[i]={}
  for j=1,N do
    A[i][j]=io.read("n")
  end
end
local total={}
for i=1,N do
  local a1=0
  local a2=0
  for j=1,i do
    a1=a1+A[1][j]
  end
  for k=i,N do
    a2=a2+A[2][k]
  end
  total[i]=a1+a2
end
table.sort(total)
print(total[N])