local mfl, mce, mmi = math.floor, math.ceil, math.min
local SegTree = {}
SegTree.updateAll = function(self)
  for i = self.stagenum - 1, 1, -1 do
    for j = 1, self.cnt[i] do
      self.stage[i][j] = self.func(self.stage[i + 1][j * 2 - 1], self.stage[i + 1][j * 2])
    end
  end
end
SegTree.create = function(self, n, func, emptyvalue)
  self.func, self.emptyvalue = func, emptyvalue
  local stagenum, mul = 1, 1
  self.cnt, self.stage, self.size = {1}, {{}}, {}
  while mul < n do
    mul, stagenum = mul * 2, stagenum + 1
    self.cnt[stagenum], self.stage[stagenum] = mul, {}
  end
  for i = 1, stagenum do self.size[i] = self.cnt[stagenum + 1 - i] end
  self.stagenum = stagenum
  for i = 1, mul do self.stage[stagenum][i] = i end
  self:updateAll()
end
SegTree.getRange = function(self, left, right)
  if left == right then return self.stage[self.stagenum][left] end
  local start_stage = 1
  while right - left + 1 < self.size[start_stage] do
    start_stage = start_stage + 1
  end
  local ret = self.emptyvalue
  local t1, t2, t3 = {start_stage}, {left}, {right}
  while 0 < #t1 do
    local stage, l, r = t1[#t1], t2[#t1], t3[#t1]
    table.remove(t1) table.remove(t2) table.remove(t3)
    local sz = self.size[stage]
    if (l - 1) % sz ~= 0 then
      local newr = mmi(r, mce((l - 1) / sz) * sz)
      table.insert(t1, stage + 1) table.insert(t2, l) table.insert(t3, newr)
      l = newr + 1
    end
    if sz <= r + 1 - l then
      ret = self.func(ret, self.stage[stage][mce(l / sz)])
      l = l + sz
    end
    if l <= r then
      table.insert(t1, stage + 1) table.insert(t2, l) table.insert(t3, r)
    end
  end
  return ret
end
SegTree.update = function(self, idx)
  for i = self.stagenum - 1, 1, -1 do
    local dst = mce(idx / 2)
    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.top = function(self) return self.stage[1][1] end
SegTree.new = function(n, func, emptyvalue)
  local obj = {}
  setmetatable(obj, {__index = SegTree})
  obj:create(n, func, emptyvalue)
  return obj
end

local n, m = io.read("*n", "*n")
local edge = {}
local updated = {}
local vmin, vmax = {}, {}
for i = 1, n do
  edge[i] = {}
  updated[i] = true
  vmin[i] = 1
  vmax[i] = 1000000000 - 1
end
updated[n + 1] = false
vmin[n + 1], vmax[n + 1] = 1, 1000000000 - 1
for i = 1, m do
  local a, b, c = io.read("*n", "*n", "*n")
  edge[a][b] = c
  edge[b][a] = c
  vmax[a] = c - 1
  vmax[b] = c - 1
end
local function merge(a, b)
  if not updated[a] and not updated[b] then return n + 1
  elseif not updated[a] then return b
  elseif not updated[b] then return a end
  return vmax[a] - vmin[a] < vmax[b] - vmin[b] and a or b
end
local st = SegTree.new(n, merge, n + 1)
while true do
  local src = st:top()
  if n < src then break end
  updated[src] = false
  st:update(src)
  local srcmin, srcmax = vmin[src], vmax[src]
  for dst, sum in pairs(edge[src]) do
    local f = false
    if vmin[dst] < sum - srcmax then
      vmin[dst] = sum - srcmax
      f = true
    end
    if sum - srcmin < vmax[dst] then
      vmax[dst] = sum - srcmin
      f = true
    end
    if f then
      updated[dst] = true
      st:update(dst)
    end
  end
end
print(math.max(0, vmax[1] - vmin[1] + 1))
