#!/usr/bin/env python3
# from typing import *

import sys
import io
import math
import collections
import decimal
import itertools
import bisect
import heapq


def input():
    return sys.stdin.readline()[:-1]


# sys.setrecursionlimit(1000000)

# _INPUT = """5 3
# 1 3 1
# 3 5 3
# 4 5 4

# """
# sys.stdin = io.StringIO(_INPUT)

INF = 10**10

class SegTree_Update_QRMin:
    def __init__(self, a) -> None:
        n = len(a)
        self.n0 = 1 << (n-1).bit_length()
        self.data = ([INF] * self.n0) + a + ([INF] * (self.n0-n))
        for i in reversed(range(1, self.n0)):
            self.data[i] = min(self.data[i*2], self.data[i*2+1])
    def query_rmin(self, l, r):
        l += self.n0
        r += self.n0
        s = INF
        while l < r:
            if l & 1:
                s = min(s, self.data[l])
                l += 1
            if r & 1:
                s = min(s, self.data[r-1])
                r -= 1
            l >>= 1
            r >>= 1
        return s
    def update(self, i, x):
        i += self.n0
        self.data[i] = x
        while i > 0:
            i >>= 1
            self.data[i] = min(self.data[i*2], self.data[i*2+1])
    def get_value(self, i) -> int:
        return self.data[i+self.n0]

def solve(N, Q, Query):
    Query.sort(key=lambda x: (x[1], x[0], x[2]))
    result = [10**9] * N
    k = 0
    for i in range(N):
        if k < Q:
            l, r, b = Query[k]
            if l <= i <= r:
                result[i] = b
                k += 1
            elif r < i:
                return [-1]
    
    seg_tree = SegTree_Update_QRMin(result)
    for l, r, b in Query:
        if seg_tree.query_rmin(l, r+1) != b:
            return [-1]
    return result


N, Q = map(int, input().split())
Query = []
for _ in range(Q):
    l, r, b = map(int, input().split())
    Query.append((l-1, r-1, b))

print(*solve(N, Q, Query))