import times, strutils, sequtils, math, algorithm, tables, sets, lists, intsets
import critbits, future, strformat, deques,heapqueue
template `max=`(x,y) = x = max(x,y)
template `min=`(x,y) = x = min(x,y)
template `mod=`(x,y) = x = x mod y
template scan2 = (scan(), scan())
template scan3 = (scan(), scan())
let read* = iterator: string {.closure.} =
    while true: (for s in stdin.readLine.split: yield s)
proc scan(): int = read().parseInt
proc scanf(): float = read().parseFloat
proc toInt(c:char): int =
    return int(c) - int('0')


const maxn = 500
var
  board:array[maxn,array[maxn,int]]
  costS:array[maxn,array[maxn,int]]
  costG:array[maxn,array[maxn,int]]
  fromS:array[maxn,array[maxn,(int,int)]]
  fromG:array[maxn,array[maxn,(int,int)]]

proc onCompile()=
  for i in 0..<maxn:
    for j in 0..<maxn:
      board[i][j]=0
      costS[i][j]=int.high.div(4)
      costG[i][j]=int.high.div(4)

onCompile()

proc solve():int=
  var
    n = scan()
    m = scan()
    #board = newseqwith(n,newseqwith(n,0))
    #costS = newseqwith(n,newseqwith(n,int.high.div(4)))
    #costG = newseqwith(n,newseqwith(n,int.high.div(4)))
    #fromS = newseqwith(n,newseq[(int,int)](n))
    #fromG = newseqwith(n,newseq[(int,int)](n))
  costS[0][0]=0
  costG[n-1][n-1]=0
  for i in 0..<m:
    var
      (h,w,c)=(scan()-1,scan()-1,scan())
    board[h][w]=c
  var
    q = initHeapQueue[(int,int,int)]()
  q.push((0,0,0))
  #var fix = n^2
  #var touch = newseqwith(n,newseqwith(n,false))
  while q.len>0:
    var
      (c,h,w)=q.pop()
    #if touch[h][w]==false:
      ##touch[h][w] = true
      #fix-=1
      #if fix==0:
        #break
    if c > costS[h][w]:continue
    if h-1>=0:
      if costS[h-1][w] > costS[h][w]+board[h-1][w]+1:
        costS[h-1][w] = costS[h][w]+board[h-1][w]+1
        q.push((costS[h-1][w],h-1,w))
        fromS[h-1][w] = ((h,w))
    if h+1<n:
      if costS[h+1][w] > costS[h][w]+board[h+1][w]+1:
        costS[h+1][w] = costS[h][w]+board[h+1][w]+1
        q.push((costS[h+1][w],h+1,w))
        fromS[h+1][w] = ((h,w))
      
    if w-1>=0:
      if costS[h][w-1] > costS[h][w]+board[h][w-1]+1:
        costS[h][w-1] = costS[h][w]+board[h][w-1]+1
        q.push((costS[h][w-1],h,w-1))
        fromS[h][w-1] = ((h,w))
      
    if w+1<n:
      if costS[h][w+1] > costS[h][w]+board[h][w+1]+1:
        costS[h][w+1] = costS[h][w]+board[h][w+1]+1
        q.push((costS[h][w+1],h,w+1))
        fromS[h][w+1] = ((h,w))
  q.clear()
  q.push((0,n-1,n-1))
  #fix = n^2
  #touch = newseqwith(n,newseqwith(n,false))
  #echo "往路"
  while q.len>0:
    var
      (c,h,w)=q.pop()
    if c > costG[h][w]:continue
    #if touch[h][w]==false:
      #touch[h][w] = true
      #fix-=1
      #if fix==0:
        #break
    if h-1>=0:
      if costG[h-1][w] > costG[h][w]+board[h-1][w]+1:
        costG[h-1][w] = costG[h][w]+board[h-1][w]+1
        q.push((costG[h-1][w],h-1,w))
        fromG[h-1][w] = ((h,w))
    if h+1<n:
      if costG[h+1][w] > costG[h][w]+board[h+1][w]+1:
        costG[h+1][w] = costG[h][w]+board[h+1][w]+1
        q.push((costG[h+1][w],h+1,w))
        fromG[h+1][w] = ((h,w))
      
    if w-1>=0:
      if costG[h][w-1] > costG[h][w]+board[h][w-1]+1:
        costG[h][w-1] = costG[h][w]+board[h][w-1]+1
        q.push((costG[h][w-1],h,w-1))
        fromG[h][w-1] = ((h,w))
      
    if w+1<n:
      if costG[h][w+1] > costG[h][w]+board[h][w+1]+1:
        costG[h][w+1] = costG[h][w]+board[h][w+1]+1
        q.push((costG[h][w+1],h,w+1))
        fromG[h][w+1] = ((h,w))
  #echo "復路"
  result = costS[n-1][n-1]

  for h in 0..<n:
    for w in 0..<n:
      # (h,w)に通行料金がかかる場合
      if board[h][w]>0:
        var
          (fh,fw) = fromS[h][w]
          (th,tw) = fromG[h][w]
        result.min=2+costS[fh][fw]+costG[th][tw]

    

echo solve()