import sys
import heapq


input = sys.stdin.buffer.readline


class Set_min(set):
    def __init__(self, iterable=tuple()):
        super(Set_min, self).__init__(iterable)
        self.h = list(set(iterable))
        heapq.heapify(self.h)

    def add(self, x):
        super(Set_min, self).add(x)
        heapq.heappush(self.h, x)

    def remove(self, x):
        super(Set_min, self).remove(x)

    def min(self):
        if not super(Set_min, self).__len__():
            raise ValueError
        while self.h and self.h[0] not in self:
            heapq.heappop(self.h)
        return self.h[0]


N, Q = map(int, input().split())
MAX = 10 ** 9
h = []
queries = [[] for _ in range(N + 1)]
for i in range(Q):
    l, r, b = map(int, input().split())
    l -= 1
    queries[l].append((b, i, 1))
    queries[r].append((b, i, 2))

ans = [MAX] * N
st1 = Set_min()
st2 = Set_min()
for i in range(N):
    for b, j, f in queries[i]:
        if f == 1:
            st1.add((-b, j))
        else:
            # assert f == 2
            if (-b, j) in st1:
                print(-1)
                exit()
            else:
                st2.remove((-b, j))

    if st1:
        q = st1.min()
        if st2 and -q[0] < -st2.min()[0]:
            continue
        st1.remove(q)
        ans[i] = -q[0]
        st2.add(q)

for b, j, f in queries[N]:
    if (-b, j) in st1:
        print(-1)
        exit()
print(*ans)