class WeightedUnionFind:
    def __init__(self, n):
        self.par = [i for i in range(n+1)]
        self.rank = [0] * (n+1)
        # 根への距離を管理
        self.weight = [0] * (n+1)

    # 検索
    def find(self, x):
        if self.par[x] == x:
            return x
        else:
            y = self.find(self.par[x])
            # 親への重みを追加しながら根まで走査
            self.weight[x] += self.weight[self.par[x]]
            self.par[x] = y
            return y

    # 併合
    def union(self, x, y, w):
        rx = self.find(x)
        ry = self.find(y)
        # xの木の高さ < yの木の高さ
        if self.rank[rx] < self.rank[ry]:
            self.par[rx] = ry
            self.weight[rx] = w - self.weight[x] + self.weight[y]
        # xの木の高さ ≧ yの木の高さ
        else:
            self.par[ry] = rx
            self.weight[ry] = -w - self.weight[y] + self.weight[x]
            # 木の高さが同じだった場合の処理
            if self.rank[rx] == self.rank[ry]:
                self.rank[rx] += 1

    # 同じ集合に属するか
    def same(self, x, y):
        return self.find(x) == self.find(y)

    # xからyへのコスト
    def diff(self, x, y):
        return self.weight[x] - self.weight[y]
    
def Dijkstra(s, graph):
    INF = 2 ** 63 - 1
    import heapq
    n = len(graph)
    dist = [INF] * n
    dist[s] = 0
    bef = [0] * n
    bef[s] = s
    hq = [(0, s)]
    heapq.heapify(hq)
    while hq:
        c, now = heapq.heappop(hq)
        
        if c > dist[now]:
            continue
        for to, cost in graph[now]:
            if dist[now] + cost < dist[to]:
                dist[to] = cost + dist[now]
                bef[to] = now
                heapq.heappush(hq, (dist[to], + to))
    return dist, bef

def DijkstraRest(bef, t):
    now = t
    ret = []
    while bef[now] != now:
        ret.append((bef[now], now))
        now = bef[now]
    ret.reverse()
    return ret

import sys, time, random
from collections import deque, Counter, defaultdict
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
inf = 2 ** 61 - 1
mod = 998244353

n, m = mi()

graph = [[] for _ in range(n)]
U = WeightedUnionFind(n)
EDGE = {}
cnt = 1
for _ in range(m):
    u, v, w = mi()
    u -= 1
    v -= 1
    if U.same(u, v) and U.diff(u, v) > w:
        D, r = Dijkstra(u, graph)
        rest = DijkstraRest(r, v)
        ans = []
        for i in range(len(rest)):
            ans.append(EDGE[rest[i]])
        ans.append(cnt)
        print(len(ans))
        print(u + 1)
        print(*ans)
        exit()
    elif U.same(u, v) and U.diff(u, v) < w:
        D, r = Dijkstra(v, graph)
        rest = DijkstraRest(r, u)
        ans = []
        for i in range(len(rest)):
            ans.append(EDGE[rest[i]])
        ans.append(cnt)
        print(len(ans))
        print(v + 1)
        print(*ans)
        exit()
        
    else:
        EDGE[(u, v)] = cnt
        EDGE[(v, u)] = cnt
        U.union(u, v, w)
        graph[u].append((v, 1))
        graph[v].append((u, 1))
    cnt += 1
print(-1)