import sys

# sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = (1 << 63)-1
# inf = (1 << 31)-1
# md = 10**9+7
md = 998244353

from heapq import *

n, m = LI()
cc = [0]*n*n
for _ in range(m):
    i, j, c = LI1()
    cc[i*n+j] = c+1

dist = [[inf]*n*n for _ in range(2)]
dist[0][0] = 0
hp = [(0, 0, 0)]
while hp:
    d, f, ij = heappop(hp)
    if d > dist[f][ij]: continue
    i, j = divmod(ij, n)
    for di, dj in dij:
        ni, nj = i+di, j+dj
        if ni < 0 or nj < 0 or ni >= n or nj >= n: continue
        nij = ni*n+nj
        nd = d+cc[nij]+1
        if nd >= dist[f][nij]: continue
        dist[f][nij] = nd
        heappush(hp, (nd, f, nij))
        if f == 0:
            nd = d+1
            if nd >= dist[1][nij]: continue
            dist[1][nij] = nd
            heappush(hp, (nd, 1, nij))

print(dist[1][-1])