import sys;input=sys.stdin.readline
from heapq import heappush, heappop
INF = 10**18
def dijkstra(N, G, s):
    dist = [INF] * N
    que = [(0, s)]
    dist[s] = 0
    while que:
        c, v = heappop(que)
        if dist[v] < c:
            continue
        for t, cost in G[v]:
            if dist[v] + cost < dist[t]:
                dist[t] = dist[v] + cost
                heappush(que, (dist[t], t))
    return dist
N, M = map(int, input().split())
from collections import defaultdict
D = defaultdict(int)
U = N**2
for _ in range(M):
    a, b, c = map(int, input().split())
    a-=1
    b-=1
    D[a*N+b] = c
    D[a*N+b+U] = c

G = [set() for _ in range(2*(N**2))]
for i in range(N):
    for j in range(N):
        c = i*N+j
        if j!=N-1:
            G[c].add((c+1, 1+D[c+1]))
        if j!=0:
            G[c].add((c-1, 1+D[c-1]))
        if i!=0:
            G[c].add((c-N, 1+D[c-N]))
        if i!=N-1:
            G[c].add((c+N, 1+D[c+N]))

        if j!=N-1:
            G[c].add((c+1+U, 1))
        if j!=0:
            G[c].add((c-1+U, 1))
        if i!=0:
            G[c].add((c-N+U, 1))
        if i!=N-1:
            G[c].add((c+N+U, 1))

        c += U
        if j!=N-1:
            G[c].add((c+1, 1+D[c+1]))
        if j!=0:
            G[c].add((c-1, 1+D[c-1]))
        if i!=0:
            G[c].add((c-N, 1+D[c-N]))
        if i!=N-1:
            G[c].add((c+N, 1+D[c+N]))

X = dijkstra(2*(N**2), G, 0)
print(X[-1])