import sys
import heapq

input = sys.stdin.buffer.readline

N, Q = map(int, input().split())
MAX = 10 ** 9
h = []
queries = [[] for _ in range(N)]
for _ in range(Q):
    l, r, b = map(int, input().split())
    l -= 1
    r -= 1
    queries[l].append((-b, r))

ans = [MAX] * N
for i in range(N):
    for q in queries[i]:
        heapq.heappush(h, q)
    if h:
        bm, r = heapq.heappop(h)
        if r < i: print(-1); exit()
        ans[i] = -bm
if h: print(-1);exit()
print(*ans)