import sys

# sys.setrecursionlimit(200005)
# sys.set_int_max_str_digits(1000005)
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
# md = 10**9+7
md = 998244353

from heapq import *

t=II()
n,m=LI()
to=[[] for _ in range(n)]
uvw=[]
for i in range(m):
    u,v,w=LI()
    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)