import sys
import bisect
from heapq import *

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

INF = 1 << 60

T = int(readline())
N, M = map(int, readline().split())
G = []
for e in range(M):
    u, v, c = map(int, readline().split())
    G.append((u, v, c))
    if T == 0:
        G.append((v, u, c))
G.sort()
frm = [g[0] for g in G]
idx = [bisect.bisect_left(frm, v) for v in range(N + 2)]

def dijkstra(S, T):
    dist = [INF] * (N + 1)
    dist[S] = 0
    q = [0 << 15 | S]
    while q:
        dv, v = divmod(heappop(q), 1 << 15)
        if dv > dist[v]:
            continue
        if v == T:
            return dv
        for e in range(idx[v], idx[v + 1]):
            _, w, c = G[e]
            if (v, w) == (S, T):
                continue
            dw = dv + c
            if dist[w] > dw:
                dist[w] = dw
                heappush(q, dw << 15 | w)
    return INF

def main():
    done = set()
    ans = INF
    for u, v, c in G:
        if (u, v) in done:
            continue
        done.add((u, v))
        done.add((v, u))
        x = dijkstra(v, u)  # v から u に、直接ではない行く
        x = x + c  # cycle length
        ans = min(ans, x)
    if ans == INF:
        ans = -1
    return ans

print(main())