from heapq import heappush, heappop
import sys
def input():
	return sys.stdin.buffer.readline()[:-1]

def enc(pos, cost):
	return cost * 10000 + pos

def dec(x):
	return x % 10000, x // 10000

INF = 10**15
t = int(input())
n, m = map(int, input().split())
adj = [[] for _ in range(n)]
for _ in range(m):
	u, v, w = map(int, input().split())
	adj[u-1].append(enc(v-1, w))
	if t == 0:
		adj[v-1].append(enc(u-1, w))

ans = INF
for x in range(n):
	dist = [INF for _ in range(n)]
	prev = [-1 for _ in range(n)]
	dist[x] = 0
	q = [x]
	while q:
		i, c0 = dec(heappop(q))
		#print(i, c0)
		for y in adj[i]:
			j, c1 = dec(y)
			if t == 0 and prev[i] == j:
				continue
			if dist[j] > c0 + c1:
				prev[j] = i
				dist[j] = c0 + c1
				heappush(q, enc(j, c0 + c1))
			else:
				#print("! " + str(j) + " " + str(c1))
				if t == 0 or j == x:
					ans = min(ans, c0 + dist[j] + c1)
	#print("-----")

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