import sys

input = sys.stdin.buffer.readline

def MI(): return map(int, input().split())
dij = [(1, 0), (0, 1), (-1, 0), (0, -1)]

from heapq import *

inf = 10**16
n, m = MI()
cc = [[0]*n for _ in range(n)]
for _ in range(m):
    i, j, c = MI()
    cc[i-1][j-1] = c

hp = []
dd = [[[inf]*2 for _ in range(n)] for _ in range(n)]
dd[0][0][0] = 0
heappush(hp, (0, 0, 0, 0))
while hp:
    d, i, j, k = heappop(hp)
    if (i,j)==(n-1,n-1):
        print(d)
        exit()
    if d > dd[i][j][k]: continue
    for di, dj in dij:
        ni, nj = i+di, j+dj
        if ni < 0 or ni >= n or nj < 0 or nj >= n: continue
        nd = d+cc[ni][nj]+1
        if nd < dd[ni][nj][k]:
            dd[ni][nj][k] = nd
            heappush(hp, (nd, ni, nj, k))
        if k == 0 and d+1 < dd[ni][nj][1]:
            dd[ni][nj][1] = d+1
            heappush(hp, (d+1, ni, nj, 1))