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

#和のセグ木にするときは以下の関数を定義する必要あり。
def segfunc(x,y):
  return x+y

class SegmentTree(object):
    def __init__(self, A, dot, unit):
        n = 1 << (len(A) - 1).bit_length()
        tree = [unit] * (2 * n)
        for i, v in enumerate(A):
            tree[i + n] = v
        for i in range(n - 1, 0, -1):
            tree[i] = dot(tree[i << 1], tree[i << 1 | 1])
        self._n = n
        self._tree = tree
        self._dot = dot
        self._unit = unit

    def __getitem__(self, i):
        return self._tree[i + self._n]

    def update(self, i, v):
        i += self._n
        self._tree[i] = v
        while i != 1:
            i >>= 1
            self._tree[i] = self._dot(self._tree[i << 1], self._tree[i << 1 | 1])

    def add(self, i, v):
        self.update(i, self[i] + v)

    def sum(self, l, r): #これで[l,r)から取り出す。
        l += self._n
        r += self._n
        l_val = r_val = self._unit
        while l < r:
            if l & 1:
                l_val = self._dot(l_val, self._tree[l])
                l += 1
            if r & 1:
                r -= 1
                r_val = self._dot(self._tree[r], r_val)
            l >>= 1
            r >>= 1
        return self._dot(l_val, r_val)

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
    #十分条件をチェック
    Tree = SegmentTree(ans,min,INF)
    for l,r,b in query:
        if Tree.sum(l,r+1) == b: continue
        else:
            print(-1);break
    else:
        print(*ans)

if __name__ == '__main__':
    main()