local bls, brs = bit.lshift, bit.rshift
local Heapq = {}
Heapq.create = function(self, lt)
  self.lt = lt
  self.cnt = 0
  self.t = {}
end

Heapq.empty = function(self)
  return 0 == self.cnt
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.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", "*l")
local t = {}
local tpos = {}
for i = 1, n do
  local s = io.read()
  t[i] = {}
  for j = 1, #s do
    t[i][j] = s:byte(j) - 96
  end
  tpos[i] = 1
end

local hq = Heapq.new(function(a, b)
  if #t[b] < tpos[b] then return true end
  if #t[a] < tpos[a] then return false end
  return t[a][tpos[a]] < t[b][tpos[b]]
end)
for i = 1, n do
  hq:push(i)
end
local ret = {}
while not hq:empty() do
  local idx = hq:pop()
  table.insert(ret, t[idx][tpos[idx]])
  tpos[idx] = tpos[idx] + 1
  if tpos[idx] <= #t[idx] then hq:push(idx) end
end
for i = 1, #ret do
  ret[i] = string.char(ret[i] + 96)
end
print(table.concat(ret))