local bls, brs = bit.lshift, bit.rshift
local Heapq = {}
Heapq.create = function(self, lt)
  self.lt = lt
  self.cnt = 0
  self.t = {}
end
Heapq.push = function(self, v)
  local hqlt = self.lt
  local hqt = self.t
  local c = self.cnt + 1
  self.cnt = c
  hqt[c] = v
  while 1 < c do
    local p = brs(c, 1)
    if hqlt(hqt[c], hqt[p]) then
      hqt[c], hqt[p] = hqt[p], hqt[c]
      c = p
    else
      break
    end
  end
end
Heapq.empty = function(self)
  return self.cnt == 0
end
Heapq.top = function(self)
  return self.t[1]
end

Heapq.pop = function(self)
  local hqlt = self.lt
  local hqt = self.t
  local ret = hqt[1]
  local c = self.cnt
  hqt[1] = hqt[c]
  c = c - 1
  self.cnt = c
  local p = 1
  while true do
    local d1, d2 = p * 2, p * 2 + 1
    if c < d1 then break
    elseif c < d2 then
      if hqlt(hqt[d1], hqt[p]) then
        hqt[d1], hqt[p] = hqt[p], hqt[d1]
      end
      break
    else
      if hqlt(hqt[d1], hqt[d2]) then
        if hqlt(hqt[d1], hqt[p]) then
          hqt[d1], hqt[p] = hqt[p], hqt[d1]
          p = d1
        else break
        end
      else
        if hqlt(hqt[d2], hqt[p]) then
          hqt[d2], hqt[p] = hqt[p], hqt[d2]
          p = d2
        else break
        end
      end
    end
  end
  return ret
end

Heapq.new = function(lt)
  local obj = {}
  setmetatable(obj, {__index = Heapq})
  obj:create(lt)
  return obj
end

local n = io.read("*n")
local hqadd = Heapq.new(function(a, b) return a < b end)
local hqrm = Heapq.new(function(a, b) return a < b end)
local rmtasks = {}
for i = 1, n + 1 do
  rmtasks[i] = {}
end
for i = 1, n - 1 do
  local right = io.read("*n")
  for j = 1, #rmtasks[i] do
    hqrm:push(rmtasks[i][j])
  end
  while true do
    local cont = false
    if not hqadd:empty() and not hqrm:empty() then
      if hqadd:top() == hqrm:top() then
        hqadd:pop()
        hqrm:pop()
        cont = true
      end
    end
    if not cont then break end
  end
  local cur = hqadd:empty() and 0 or hqadd:top()
  local nxt = cur + 1
  hqadd:push(nxt)
  table.insert(rmtasks[right + 1], nxt)
end
do
  local i = n
  for j = 1, #rmtasks[i] do
    hqrm:push(rmtasks[i][j])
  end
  while true do
    local cont = false
    if not hqadd:empty() and not hqrm:empty() then
      if hqadd:top() == hqrm:top() then
        hqadd:pop()
        hqrm:pop()
        cont = true
      end
    end
    if not cont then break end
  end
  local cur = hqadd:empty() and 0 or hqadd:top()
  print(cur)
end