import sys

# sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = 10**20
md = 998244353
# md = 10**9+7

class SparseTableMin:
    def __init__(self, aa):
        w = len(aa)
        h = w.bit_length()
        table = [aa]+[[-1]*w for _ in range(h-1)]
        tablei1 = table[0]
        for i in range(1, h):
            tablei = table[i]
            for j in range(w-(1 << i)+1):
                rj = j+(1 << (i-1))
                tablei[j] = min(tablei1[j], tablei1[rj])
            tablei1 = tablei
        self.table = table

    # [l,r)の最小値
    def min(self, l, r):
        i = (r-l).bit_length()-1
        tablei = self.table[i]
        Lmin = tablei[l]
        Rmin = tablei[r-(1 << i)]
        if Lmin < Rmin: Rmin = Lmin
        return Rmin

from heapq import *

mx = 10**9

n, q = LI()
aa = [mx]*n
lrb = []
ltorb = [[] for _ in range(n+1)]
rtob = [[] for _ in range(n+1)]
for _ in range(q):
    l, r, b = LI()
    l -= 1
    lrb.append((l, r, b))
    ltorb[l].append((r, b))
    rtob[r].append(b)

hp = []
rem = []

aa = [mx]*n
for i in range(n):
    for b in rtob[i]:
        heappush(rem, -b)
    while hp and rem and hp[0] == rem[0]:
        heappop(hp)
        heappop(rem)
    for r, b in ltorb[i]:
        heappush(hp, -b)
    if not hp: continue
    aa[i] = -hp[0]

sp = SparseTableMin(aa)
for l, r, b in lrb:
    if sp.min(l, r) != b:
        print(-1)
        exit()

print(*aa)