def assert f
  unless f
    puts "Error!: Constraint Violation"
    exit
  end
end

n = gets.to_i
assert(1 <= n && n <= 300000)


pre_x = -1
pre_y = -1
dp = Hash.new(0)
same = 0
n.times do
  x,y = gets.split.map(&:to_i)
  assert(1 <= x && x <= 10**9)
  assert(1 <= y && y <= 10**9)

  ndp = Hash.new(0)
  # xi, yi の順番に置くとき
  if x == pre_x
    ndp[y] = [dp[pre_x] + x, dp[pre_y]].max
  elsif x == pre_y
    ndp[y] = [dp[pre_y] + x, dp[pre_x]].max
  else
    ndp[y] = [dp[pre_x], dp[pre_y]].max
  end

  # yi, xi の順番に置くとき
  if y == pre_x
    ndp[x] = [dp[pre_x] + y, dp[pre_y]].max
  elsif y == pre_y
    ndp[x] = [dp[pre_y] + y, dp[pre_x]].max
  else
    ndp[x] = [dp[pre_x], dp[pre_y]].max
  end

  dp = ndp
  pre_x = x
  pre_y = y

  same += x if x == y
end
puts [dp[pre_x], dp[pre_y]].max + same