import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################

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 dfs(n, e, U, V):
    g = [[] for _ in range(n)]
    for u, v, w, i in e:
        g[u].append((v, w, i))
        g[v].append((u, -w, i))
    
    prev_v = [-1] * n
    prev_e = [-1] * n
    seen = [False] * n
    q = [U]
    seen[U] = True
    while q:
        x = q.pop()
        for y, w, i in g[x]:
            if seen[y]:
                continue
            seen[y] = True
            prev_v[y] = x
            prev_e[y] = i
            q.append(y)
    
    path = []
    x = V
    while x != U:
        path.append(prev_e[x])
        x = prev_v[x]
    
    return path[::-1]

n, m = na()
e = []
for i in range(m):
    u, v, w = na()
    e.append((u-1, v-1, w, i))

wuf = WeightedUnionFind(n)

for u, v, w, i in e:
    if wuf.same(u, v):
        if wuf.diff(u, v) > w:
            path = dfs(n, e[:i], u, v)
            print(len(path) + 1)
            print(u+1)
            print(*([path[i]+1 for i in range(len(path))] + [i+1]))
            exit()
        elif wuf.diff(u, v) < w:
            path = dfs(n, e[:i], v, u)
            print(len(path) + 1)
            print(v+1)
            print(*([path[i]+1 for i in range(len(path))] + [i+1]))
            exit()
    else:
        wuf.union(u, v, w)

print(-1)