import sys
input = sys.stdin.readline

# https://at274.hatenablog.com/entry/2018/02/03/140504
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]
    
    
from collections import deque
def bfs(G, s):
    Q = deque([s])
    N = len(G)
    dist = [-1] * N
    par = [-1] * N
    dist[s] = 0
    while Q:
        u = Q.popleft()
        for v, i in G[u]:
            if dist[v] != -1:
                continue
            dist[v] = dist[u] + 1
            par[v] = (u, i)
            Q.append(v)

    return par

    
N, M = map(int, input().split())
U = WeightedUnionFind(N)
flag = 1
Edge = []
start, goal = -1, -1
for i in range(M):
    u, v, w = map(int, input().split())
    u, v = u - 1, v - 1
    if U.same(u, v) and U.diff(u, v) != w:
        if U.diff(u, v) < w:
            flag = 1
        else:
            flag = 0
        start = u
        goal = v
        break
    U.union(u, v, w)
    Edge.append((u, v))

if start == -1:
    print(-1)
    exit()
    
G = [[] for i in range(N)]
for i in range(len(Edge)):
    u, v = Edge[i]
    G[u].append((v, i))
    G[v].append((u, i))
    
par = bfs(G, start)
ans = []
while goal != start:
    nv, ni = par[goal]
    ans.append(i + 1)
    goal = nv
    
ans = [len(Edge) + 1] + ans
if flag == 0:
    ans.reverse()
    
print(len(ans))
print(start + 1)
print(*ans)