O,R=print,range
J=lambda:map(int,input().split())
N,M=J()
D=[[]for i in R(N)]
E=[]
p,h=list(R(N)),[0]*N
w=h[:]
def r(i):
	m=p[i]
	while m!=p[m]:
		w[i]+=w[m]
		m=p[i]=p[m]
	return m
for j in R(M):
	A,B,W=map(int,input().split());A-=1;B-=1
	a,b=r(A),r(B)
	E+=[[A,B,W]]
	if a==b:
		if w[A]-w[B]!=W:
			P,S,F=[j+1],[A],[0]*N
			while F[B]<1:
				i=S.pop()
				for[e,m]in D[i]:
					if F[e]<1:
						F[e],p[e]=1,m
						S+=[e]
			while A!=B:
				m=p[B]
				P+=[m+1]
				if B==E[m][0]:B,W=E[m][1],W+E[m][2]
				else:B,W=E[m][0],W-E[m][2]
			O(len(P))
			O(A+1)
			exit(O(*(P[-1::-1]if W<0else P)))
	else:
		W=w[B]+W-w[A]
		if h[b]<h[a]:a,b,W=b,a,-W
		if h[a]==h[b]:h[b]+=1
		p[a],w[a]=b,W
	D[A]+=[[B,j]]
	D[B]+=[[A,j]]
O(-1)