import sys
input = sys.stdin.readline
from collections import defaultdict 
from heapq import heapify, heappop, heappush, nlargest

def main():
    N,Q = map(int,input().split()); INF = pow(10,9)
    L = defaultdict(list)
    R = defaultdict(list)
    comp = set([])
    query = []
    PQ = []
    for i in range(Q):
        l,r,b = map(int,input().split())
        l -= 1; r -= 1 #0-index
        L[l].append((b,i))
        R[r].append((b,i))
        comp.add(b)
        query.append((l,r,b))

    ans = [INF]*N
    i = 0
    PQ = []
    while i < N:
        for b,idx in L[i]:
            heappush(PQ,(-b,idx)) #-Minとクエリ番号
        if PQ:
            b,idx = heappop(PQ)
            b *= -1
            if query[idx][1] < i: #この制約を満たせていない
                print(-1);exit()
            ans[i] = b
        i += 1
    print(*ans)

    
if __name__ == '__main__':
    main()