from heapq import *
class SegTree():
    def __init__(self, n, e, ope, lst=[]):
        self.N0 = 2 ** (n - 1).bit_length()
        self.e = e
        self.ope = ope
        self.data = [e] * (2 * self.N0)
        if lst:
            for i in range(n):
                self.data[self.N0 + i] = lst[i]
            for i in range(self.N0 - 1, 0, -1):
                self.data[i] = self.ope(self.data[2 * i], self.data[2 * i + 1])
    
    def f5(self):
        for i in range(self.N0 - 1, 0, -1):
            self.data[i] = self.ope(self.data[2 * i], self.data[2 * i + 1])
                
    def update(self, i, x): #a_iの値をxに更新
        i += self.N0
        self.data[i] = x
        while i > 1:
            i >>= 1
            self.data[i] = self.ope(self.data[2 * i], self.data[2 * i + 1])
    
    def add(self, i, x):
        self.update(i, x + self.get(i))
    
    def query(self, l, r): #区間[l, r)での演算結果
        if r <= l:
            return self.e
            
        res = self.e
        l += self.N0
        r += self.N0
        while l < r:
            if l & 1:
                res = self.ope(res, self.data[l])
                l += 1
            if r & 1:
                r -= 1
                res = self.ope(res, self.data[r])
            l >>= 1
            r >>= 1
        return res
            
    
    def get(self, i): #a_iの値を返す
        return self.data[self.N0 + i]

n, q = map(int, input().split())
query = []
imos = [[] for _ in range(n + 1)]
for _ in range(q):
    l, r, b = map(int, input().split())
    query.append((l, r, b))
    imos[l - 1].append((b, 1))
    imos[r].append((b, 2))

alst = [-1] * n
hq = [-1]
rem = []
for i in range(n):
    for b, t in imos[i]:
        if t == 1:
            heappush(hq, -b)
        else:
            heappush(rem, -b)
    while rem and rem[0] == hq[0]:
        heappop(rem)
        heappop(hq)
    alst[i] = -hq[0]
    
inf = 10 ** 10
e = inf
def ope(x, y):
    return min(x, y)
seg = SegTree(n, e, ope, alst)
for l, r, x in query:
    if seg.query(l - 1, r) != x:
        print(-1)
        exit()

print(*alst)