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")
#######################################################################
def find_cycle(N, M, G):
    vis = [0] * N
    used = [0] * M
    par_v = [None] * N
    par_e = [None] * N

    for s in range(N):
        if vis[s]: continue
        stack = [(s, -1, -1)]
        while stack:
            v, p, e = stack.pop()
            if e != -1 and used[e]: continue
            if vis[v]:
                par_v[v] = p
                if e != -1:
                    par_e[v] = e
                return v, p, e, par_v, par_e
            vis[v] = 1
            if e != -1:
                par_e[v] = e
                used[e] = 1
            par_v[v] = p
            for a, e in G[v]:
                if used[e]: continue
                stack.append((a, v, e))

    return -1, -1, -1, par_v, par_e

def cycle_detection(N, M, G):
    v, p, e, par_v, par_e = find_cycle(N, M, G)
    if p == -1:
        return [], []
    else:
        cycle_v = [p]
        cycle_e = [e]
        while v != p:
            e = par_e[p]
            p = par_v[p]
            cycle_v.append(p)
            cycle_e.append(e)
        return cycle_v[::-1], cycle_e[::-1]
    

def find_cycle2(N, M, G):
    vis = [0] * N
    used = [0] * M
    par_v = [None] * N
    par_e = [None] * N
    potential = [0] * N

    for s in range(N):
        if vis[s]: continue
        stack = [(s, -1, -1, 0)]
        while stack:
            v, p, e, pot = stack.pop()
            if e != -1 and used[e]: continue
            if vis[v] and pot != potential[v]:
                par_v[v] = p
                if e != -1:
                    par_e[v] = e
                return v, p, e, par_v, par_e
            vis[v] = 1
            potential[v] = pot
            if e != -1:
                par_e[v] = e
                used[e] = 1
            par_v[v] = p
            for a, e, w in G[v]:
                if used[e]: continue
                stack.append((a, v, e, pot + w))

    return -1, -1, -1, par_v, par_e


def cycle_detection2(N, M, G):
    v, p, e, par_v, par_e = find_cycle2(N, M, G)
    #print(v, p, e, par_v, par_e)
    if p == -1:
        return [], []
    else:
        cycle_v = [p]
        cycle_e = [e]
        while v != p:
            e = par_e[p]
            p = par_v[p]
            cycle_v.append(p)
            cycle_e.append(e)
        return cycle_v[::-1], cycle_e[::-1]

n, m = na()

g = [[] for i in range(n)]
E = []
for i in range(m):
    a, b, w = na()
    g[a-1].append((b-1, i, w))
    g[b-1].append((a-1, i, -w))
    E.append((a-1, b-1, w))

cycle_v, cycle_e = cycle_detection2(n, m, g)
#print(cycle_v, cycle_e)
if not cycle_v:
    print(-1)
else:
    print(len(cycle_v))
    ans = 0
    c = 0
    for i in cycle_e:
        if E[i][0] == c:
            ans += E[i][2]
            c = E[i][1]
        else:
            ans -= E[i][2]
            c = E[i][0]
    #print(ans)
    if ans > 0:
        print(cycle_v[0]+1)
        print(*[i+1 for i in cycle_e])
    else:
        print(cycle_v[0]+1)
        print(*[i+1 for i in cycle_e[::-1]])