from heapq import heapify, heappop, heappush
N,M = map(int,input().split()); INF = float("inf")
dic = {}
for i in range(M):
  h,w,c = map(int,input().split())
  h-=1;w-=1
  dic[h*N+w] = c
#print(dic)  
G = [[] for _ in range(N*N)]
dxdy = [(0,1),(0,-1),(1,0),(-1,0)]
for i in range(N):
  for j in range(N):
    now = i*N + j
    for k in range(4):
      ni = i+dxdy[k][0]
      nj = j+dxdy[k][1]
      if 0<=ni<N and 0<=nj<N:
        nxt = ni*N+nj
        if nxt in dic:
          G[now].append((1+dic[nxt],nxt))
        else:
          G[now].append((1,nxt))
#print(G)

def dijkstra_heap2(s,G):
  #S:start, V: node, E: Edge, G: Graph
  V = len(G)
  d = [INF for _ in range(2*V)] #d[i][j];j=0権利を行使していないj=1どこかで権利を行使済み
  #行使済みの点は i + V (V~2*V-1)、未行使の点はi (0~V-1)
  d[s] = 0; d[s+V] = 0
  PQ = []
  heappush(PQ,(0,s)) #コスト0,初期点s,権利行使していない
  
  while PQ:
    c,v = heappop(PQ)
    if d[v] < c:
      continue
    d[v] = c
    if v >= V:
      oriv = v - V
    else:
      oriv = v
    for cost,u in G[oriv]:
      if v < V: #未行使
        if d[u] <= cost + d[v]:
          pass
        else:
          d[u] = cost + d[v]
          heappush(PQ,(d[u], u))
        if d[u+V] <= 1 + d[v]: #移動の1は必ずかかる。
          pass
        else:
          d[u+V] = 1 + d[v]
          heappush(PQ,(d[u+V], u+V))
      else: #行使済み
        if d[u+V] <= cost + d[v]:
          pass
        else:
          d[u+V] = cost + d[v]
          heappush(PQ,(d[u+V], u+V))
  
  return d

D = dijkstra_heap2(0,G)
#print(D)
ans = min(D[N*N-1],D[2*N*N-1])

print(ans)