N, Q = list(map(int, input().split()))
B = []
ans = [0]*N
for _ in range(Q):
    l,r,b = list(map(int, input().split()))
    B.append([b,l,r])
same = set()
B.sort(reverse=True)
for i in range(Q):
    b,l,r = B[i]
    flag=False
    for j in range(l-1,r):
        if ans[j]:
            if b in same:
                flag=True
            continue
        else:
            ans[j]=b
            flag=True
    if not flag:
        print(-1)
        exit()
    same.add(b)
for i in range(N):
    if ans[i]==0:
        ans[i]=10**10
print(*ans)