inf = (1 << 63)-1

from heapq import *

t=int(input())
n,m=map(int,input().split())
to=[[] for _ in range(n)]
uvw=[]
for i in range(m):
    u,v,w=map(int,input().split())
    u,v=u-1,v-1
    to[u].append((v,w,i))
    if t==0:
        to[v].append((u,w,i))
    uvw.append((u,v,w))

def solve(s,g,lim):
    dd=[inf]*n
    hp=[]
    heappush(hp,(0,s))
    dd[s]=0
    while hp:
        d,u=heappop(hp)
        if u==g:return d
        if d>dd[u]:continue
        for v,w,i in to[u]:
            if fin[i]:continue
            if dd[v]<=d+w or d+w>=lim:continue
            dd[v]=d+w
            heappush(hp,(d+w,v))
    return inf

fin=[False]*m
ans=inf
for i,(u,v,w) in enumerate(uvw):
    if fin[i]:continue
    fin[i]=True
    ret=solve(v,u,ans-w)+w
    if ret<ans:ans=ret

if ans==inf:print(-1)
else:print(ans)