from collections import defaultdict
from heapq import heappush, heappop


def dijkstra(n: int, sv, adj):
    dists = [INF] * n
    dists[sv] = 0
    q = [(0, sv)]
    while q:
        d, v = heappop(q)
        if dists[v] != d: continue

        for to, w in adj[v]:
            nd = dists[v] + w
            if dists[to] > nd:
                dists[to] = nd
                heappush(q, (nd, to))

    return dists


INF = 1 << 62

T = int(input())
N, M = map(int, input().split())

edges = []
for _ in range(M):
    U, V, W = map(int, input().split())
    U -= 1
    V -= 1
    edges.append((U, V, W))


def solve_undirected():
    res = INF

    adj = defaultdict(list)
    edge2w = {}
    for u, v, w in edges:
        adj[u].append((v, w))
        adj[v].append((u, w))
        edge2w[u, v] = w

    used = set()
    for i in range(N):  # 頂点 i を始点とする最短経路を求める
        # if i in used: continue

        dists = dijkstra(N, i, adj)
        for j in range(N):
            if dists[j] == INF: continue

            if (j, i) in edge2w:
                res = min(res, dists[j] + edge2w[(j, i)])

    return res


def solve_directed():
    res = INF

    adj = defaultdict(list)
    edge2w = {}
    for u, v, w in edges:
        adj[u].append((v, w))
        edge2w[u, v] = w

    for i in range(N):
        # 頂点 i を始点として、各頂点への最小経路を作る
        dists = [INF] * N
        dists[i] = 0
        q = [(0, i)]
        while q:
            d, v = heappop(q)
            if dists[v] != d: continue

            for to, w in adj[v]:
                nd = dists[v] + w
                if dists[to] > nd:
                    dists[to] = nd
                    heappush(q, (nd, to))

        # 各頂点から始点 i への有向辺があるなら閉路が存在する
        for j in range(N):
            if dists[j] != INF:
                if (j, i) in edge2w:
                    res = min(res, dists[j] + edge2w[j, i])

    if res == INF:
        return -1
    return res


if T == 0:
    ans = solve_undirected()
    print(ans)
else:
    ans = solve_directed()
    print(ans)