from heapq import *
n,m=map(int,input().split())
connect=[[] for _ in range(n)]
for _ in range(m):
    a,b,c=map(int,input().split())
    a-=1
    b-=1
    connect[a].append((b,c))
    connect[b].append((a,c))
decide=[False]*n
inf=10**18
dist=[-inf]*n
dist[0]=0
que=[]
que.append((0,0))
cnt=0
while que:
    di,now=heappop(que)
    di*=-1
    if dist[now]<di:
        continue
    if decide[now]:
        continue
    decide[now]=True
    cnt+=1
    if cnt==n:
        print(dist[now]*2)
        exit()
    for to,weight in connect[now]:
        if not decide[to]:
            if dist[to]<dist[now]+weight:
                dist[to]=dist[now]+weight
                heappush(que,(-dist[to],to))