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

INF = 10**16
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(w * 3000 + v-1)
	if t == 0:
		adj[v-1].append(w * 3000 + u-1)

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:
		z = heappop(q)
		i, c0 = z % 3000, z // 3000
		for y in adj[i]:
			j, c1 = y % 3000, y // 3000
			if t == 0 and prev[i] == j:
				continue
			if dist[j] > c0 + c1:
				prev[j] = i
				dist[j] = c0 + c1
				heappush(q, j + (c0 + c1) * 3000)
			else:
				if t == 0 or j == x:
					ans = min(ans, c0 + dist[j] + c1)

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