def aa(m,seg,vv):
    while m>1:
        m//=2
        seg[m]=vv(seg[m*2],seg[m*2+1])
def bb(l,r,seg,vv,res):
    while l<r:
        if l&1:
            res=vv(res,seg[l]);l+=1
        if r&1:
            r-=1;res=vv(res,seg[r])
        l//=2;r//=2
    return res

n,q=map(int,input().split())
x=[list(map(int,input().split())) for i in range(q)]
x.sort(key=lambda x:x[2],reverse=True)
ans=[0]*n
v=1<<n.bit_length()
seg1=[-1]*v*2
seg2=[1<<30]*v*2
for i in range(n):
    seg1[i+v]=i;aa(i+v,seg1,max)
for l,r,i in x:
    while 1:
        c=bb(l+v-1,r+v,seg1,max,-1)
        if c==-1:
            break
        ans[c]=i;seg1[c+v]=-1;aa(c+v,seg1,max)
        seg2[c+v]=i;aa(c+v,seg2,min)
    if bb(l+v-1,r+v,seg2,min,1<<30)!=i:
    	print(-1)
    	exit()
for i in range(n):
    if ans[i]:
        continue
    ans[i]=1
print(" ".join(map(str,ans)))