import times, strutils, sequtils, math, algorithm, tables, sets, lists, intsets
import critbits, future, strformat, deques
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')




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[^1][^1]=0
  for i in 0..<m:
    var
      (h,w,c)=(scan()-1,scan()-1,scan())
    board[h][w]=c
  var
    q = initDeque[(int,int)]()
  q.addLast((0,0))
  while q.len>0:
    var
      (h,w)=q.popFirst()
    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.addLast((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.addLast((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.addLast((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.addLast((h,w+1))
        fromS[h][w+1] = ((h,w))
  q.addLast((n-1,n-1))
  while q.len>0:
    var
      (h,w)=q.popFirst()
    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.addLast((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.addLast((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.addLast((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.addLast((h,w+1))
        fromG[h][w+1] = ((h,w))
      
    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()