from operator import itemgetter
from itertools import *
from bisect import *
from collections import *
from heapq import *
import sys

# input=sys.stdin.buffer.readline
input=sys.stdin.readline

sys.setrecursionlimit(10**6)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(input())
def MI(): return map(int, input().split())
def MI1(): return map(int1, input().split())
def LI(): return list(map(int, input().split()))
def LI1(): return list(map(int1, input().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def SI(): return input()[:-1]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
dij = [(1, 0), (0, 1), (-1, 0), (0, -1)]

from heapq import *

def inval(ni,nj,h,w):
    if ni<0 or ni>=h or nj<0 or nj>=w:return True
    return False

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 d>dd[i][j][k]:continue
    for di,dj in dij:
        ni,nj=i+di,j+dj
        if inval(ni,nj,n,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))

print(dd[n-1][n-1][1])