local mfl, mce = math.floor, math.ceil
local mmi, mma = math.min, math.max
local bls, brs = bit.lshift, bit.rshift
local SegTree = {}
SegTree.updateAll = function(self)
  for i = self.stagenum - 1, 1, -1 do
    local cnt = bls(1, i - 1)
    for j = 1, cnt do
      self.stage[i][j] = self.func(self.stage[i + 1][j * 2 - 1], self.stage[i + 1][j * 2])
    end
  end
end
SegTree.clearAll = function(self)
  for i = self.stagenum, 1, -1 do
    local cnt = bls(1, i - 1)
    for j = 1, cnt do
      self.stage[i][j] = self.emptyvalue
    end
  end
end
SegTree.create = function(self, n, func, emptyvalue)
  self.func, self.emptyvalue = func, emptyvalue
  local stagenum, mul = 1, 1
  self.stage = {{}}
  while mul < n do
    mul, stagenum = mul * 2, stagenum + 1
    self.stage[stagenum] = {}
  end
  self.stagenum = stagenum
  self.left_stage = {}
  for i = 1, n do
    local sp, sz = 1, bls(1, stagenum - 1)
    while(i - 1) % sz ~= 0 do
      sp, sz = sp + 1, brs(sz, 1)
    end
    self.left_stage[i] = sp
  end
  self.sz_stage = {}
  local tmp, sp = 1, stagenum
  for i = 1, n do
    if tmp * 2 == i then tmp, sp = tmp * 2, sp - 1 end
    self.sz_stage[i] = sp
  end
  for i = 1, mul do self.stage[stagenum][i] = emptyvalue end
  self:updateAll()
end
SegTree.getRange = function(self, left, right)
  if left == right then return self.stage[self.stagenum][left] end
  local stagenum = self.stagenum
  local ret = self.emptyvalue
  while left <= right do
    local stage = mma(self.left_stage[left], self.sz_stage[right - left + 1])
    local sz = bls(1, stagenum - stage)
    ret = self.func(ret, self.stage[stage][1 + brs(left - 1, stagenum - stage)])
    left = left + sz
  end
  return ret
end
SegTree.update = function(self, idx)
  for i = self.stagenum - 1, 1, -1 do
    local dst = brs(idx + 1, 1)
    local rem = dst * 4 - 1 - idx
    self.stage[i][dst] = self.func(self.stage[i + 1][idx], self.stage[i + 1][rem])
    idx = dst
  end
end
SegTree.setValue = function(self, idx, value, silent)
  self.stage[self.stagenum][idx] = value
  if not silent then
    self:update(idx)
  end
end

SegTree.right_bound = function(self, val, left, right)
  local ret, retpos = self.emptyvalue, left - 1
  local l, r = left, right
  local stage = mma(self.left_stage[left], self.sz_stage[right - left + 1])
  local stagenum = self.stagenum
  while true do
    local sz = bls(1, stagenum - stage)
    local tmp = self.func(ret, self.stage[stage][mce(l / sz)])
    if tmp < val then
      ret, retpos = tmp, l + sz - 1
      if retpos == right then break end
      if l + sz <= r then
        l = l + sz
        stage = mma(self.left_stage[l], self.sz_stage[r - l + 1])
      else break end
    else
      if sz ~= 1 then stage, r = stage + 1, l + sz - 2
      else break end
    end
  end
  return retpos + 1
end

SegTree.new = function(n, func, emptyvalue)
  local obj = {}
  setmetatable(obj, {__index = SegTree})
  obj:create(n, func, emptyvalue)
  return obj
end

local n = io.read("*n")
local a = {}
local as = {}
local amap = {}
for i = 1, n do
  a[i] = io.read("*n")
  as[i] = a[i]
end
table.sort(as)
for i = 1, n do
  amap[as[i]] = i
end

local inf = 1000000007
local leftmin = {a[1]}
for i = 2, n do
  leftmin[i] = mmi(a[i], leftmin[i - 1])
end
local rightmin = {}
for i = 1, n do rightmin[i] = 0 end
rightmin[n] = a[n]
for i = n - 1, 1, -1 do
  rightmin[i] = mmi(a[i], rightmin[i + 1])
end
local ret = inf
for i = 2, n - 1 do
  if leftmin[i - 1] < a[i] and rightmin[i + 1] < a[i] then
    ret = mmi(ret, leftmin[i - 1] + a[i] + rightmin[i + 1])
  end
end

local st = SegTree.new(n, bit.bor, 0)
st:setValue(amap[a[1]], 1)
local left = {}
left[1] = inf
for i = 2, n - 1 do
  local lb = st:right_bound(1, amap[a[i]], n)
  if lb <= n then
    left[i] = as[lb]
  else
    left[i] = inf
  end
  st:setValue(amap[a[i]], 1)
end
st:clearAll()
st:setValue(amap[a[n]], 1)
for i = n - 1, 2, -1 do
  local lb = st:right_bound(1, amap[a[i]], n)
  if lb <= n and left[i] < inf then
    ret = mmi(ret, a[i] + left[i] + as[lb])
  end
  st:setValue(amap[a[i]], 1)
end
print(ret < inf and ret or -1)