N,Q = map(int, input().split())
L = []
inf = 10**9
for _ in range(Q):
    l,r,b=map(int, input().split())
    L.append([l-1,r-1,b])
L = sorted(L, key=lambda x: x[1])
L = sorted(L, key=lambda x: x[2])
L = sorted(L, key=lambda x: x[0])
ANS = [inf]*N
for l in L:
    l,r,b = l[0],l[1],l[2]
    for i in range(l,r+1):
        if ANS[i]==b:
            break
        if ANS[i]<b:
            print(-1)
            exit()
        if ANS[i]==inf:
            ANS[i]=b
            break
    else:
        print(-1)
        exit()
print(*ANS)