// -*- coding:utf-8-unix -*-
// #![feature(map_first_last)]
#![allow(dead_code)]
#![allow(unused_imports)]
#![allow(unused_macros)]
use std::collections::*;
use std::convert::*;
use std::convert::{From, Into};
use std::f64::consts::PI;
use std::fmt::Debug;
use std::fs::File;
use std::io::prelude::*;
use std::io::*;
use std::marker::Copy;
use std::mem::*;
use std::ops::Bound::*;
use std::ops::{Add, Mul, Neg, Sub};
use std::str;
use std::vec;
use std::{cmp, process::Output};
use std::{cmp::Ordering, env::consts::DLL_PREFIX};
const INF: i64 = 1223372036854775807;
const UINF: usize = INF as usize;
const FINF: f64 = 122337203685.0;
const INF128: i128 = 1223372036854775807000000000000;
const LINF: i64 = 2147483647;
const MOD: i64 = 1000000007;
// const MOD: i64 = 998244353;
const T: bool = true;
const F: bool = false;

const MPI: f64 = 3.14159265358979323846264338327950288f64;
// const MOD: i64 = INF;

const UMOD: usize = MOD as usize;
use std::cmp::*;
use std::collections::*;
use std::io::stdin;
use std::io::stdout;
use std::io::Write;

macro_rules! p {
    ($x:expr) => {
        println!("{}", $x);
    };
}
macro_rules! d {
    ($x:expr) => {
        println!("{:?}", $x);
    };
}
macro_rules! dd {
    (x:expr) => {
        dbg!(x);
    };
}

macro_rules! chmin {
    ($base:expr, $($cmps:expr),+ $(,)*) => {{
        let cmp_min = min!($($cmps),+);
        if $base > cmp_min {
            $base = cmp_min;
            true
        } else {
            false
        }
    }};
}

macro_rules! chmax {
    ($base:expr, $($cmps:expr),+ $(,)*) => {{
        let cmp_max = max!($($cmps),+);
        if $base < cmp_max {
            $base = cmp_max;
            true
        } else {
            false
        }
    }};
}

macro_rules! min {
    ($a:expr $(,)*) => {{
        $a
    }};
    ($a:expr, $b:expr $(,)*) => {{
        std::cmp::min($a, $b)
    }};
    ($a:expr, $($rest:expr),+ $(,)*) => {{
        std::cmp::min($a, min!($($rest),+))
    }};
}

macro_rules! max {
    ($a:expr $(,)*) => {{
        $a
    }};
    ($a:expr, $b:expr $(,)*) => {{
        std::cmp::max($a, $b)
    }};
    ($a:expr, $($rest:expr),+ $(,)*) => {{
        std::cmp::max($a, max!($($rest),+))
    }};
}

// use str::Chars;

// use str::Chars;
#[allow(dead_code)]
fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

#[allow(dead_code)]
fn readi() -> (i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    iter.next().unwrap().parse::<i64>().unwrap()
}

#[allow(dead_code)]
fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}
#[allow(dead_code)]
fn read_mat<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}

#[allow(dead_code)]
fn readii() -> (i64, i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
    )
}

fn readff() -> (f64, f64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<f64>().unwrap(),
        iter.next().unwrap().parse::<f64>().unwrap(),
    )
}

#[allow(dead_code)]
fn readiii() -> (i64, i64, i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
    )
}
#[allow(dead_code)]
fn readuu() -> (usize, usize) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
    )
}

fn readcc() -> (char, char) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<char>().unwrap(),
        iter.next().unwrap().parse::<char>().unwrap(),
    )
}

#[allow(dead_code)]
fn readuuu() -> (usize, usize, usize) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
    )
}

#[allow(dead_code)]
fn readuuuu() -> (usize, usize, usize, usize) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
    )
}

fn readiiii() -> (i64, i64, i64, i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
    )
}

trait SEGLazyImpl {
    type Monoid: Copy;
    type OperatorMonoid: Copy + PartialEq;
    fn m0() -> Self::Monoid;
    fn om0() -> Self::OperatorMonoid;
    fn f(x: Self::Monoid, y: Self::Monoid) -> Self::Monoid;
    fn g(x: Self::Monoid, y: Self::OperatorMonoid, weight: usize) -> Self::Monoid;
    fn h(x: Self::OperatorMonoid, y: Self::OperatorMonoid) -> Self::OperatorMonoid;
}

struct SEGLazy<T: SEGLazyImpl> {
    n: usize,
    data: Vec<T::Monoid>,
    lazy: Vec<T::OperatorMonoid>,
    weight: Vec<usize>,
}

impl<T: SEGLazyImpl> SEGLazy<T> {
    pub fn new(n: usize, init: T::Monoid) -> SEGLazy<T> {
        let weights = vec![1; n];
        Self::with_weight(n, init, weights)
    }
    pub fn with_weight(n: usize, init: T::Monoid, weights: Vec<usize>) -> Self {
        let mut m = 1;
        while m < n {
            m *= 2;
        }
        SEGLazy {
            n: m,
            data: vec![init; m * 2],
            lazy: vec![T::om0(); m * 2],
            weight: Self::mk_weight(&weights),
        }
    }
    fn mk_weight(xs: &[usize]) -> Vec<usize> {
        let n = xs.len();
        let mut m = 1;
        while m < n {
            m *= 2;
        }
        let mut res = vec![0; 2 * m];
        for i in 0..n {
            res[m + i] = xs[i];
        }
        for k in (1..m).rev() {
            let l = 2 * k;
            let r = 2 * k + 1;
            res[k] = res[l] + res[r];
        }
        res
    }
    fn propagate(&mut self, k: usize) {
        let weight = self.weight[k];
        if self.lazy[k] != T::om0() {
            if k < self.n {
                self.lazy[2 * k + 0] = T::h(self.lazy[2 * k + 0], self.lazy[k]);
                self.lazy[2 * k + 1] = T::h(self.lazy[2 * k + 1], self.lazy[k]);
            }
            self.data[k] = T::g(self.data[k], self.lazy[k], weight);
            self.lazy[k] = T::om0();
        }
    }
    fn do_update(
        &mut self,
        a: usize,
        b: usize,
        x: T::OperatorMonoid,
        k: usize,
        l: usize,
        r: usize,
    ) -> T::Monoid {
        self.propagate(k);
        if r <= a || b <= l {
            self.data[k]
        } else if a <= l && r <= b {
            self.lazy[k] = T::h(self.lazy[k], x);
            self.propagate(k);
            self.data[k]
        } else {
            self.data[k] = T::f(
                self.do_update(a, b, x, 2 * k + 0, l, (l + r) >> 1),
                self.do_update(a, b, x, 2 * k + 1, (l + r) >> 1, r),
            );
            self.data[k]
        }
    }
    #[doc = "[l,r)"]
    pub fn update(&mut self, l: usize, r: usize, x: T::OperatorMonoid) -> T::Monoid {
        let n = self.n;
        self.do_update(l, r, x, 1, 0, n)
    }
    fn do_query(&mut self, a: usize, b: usize, k: usize, l: usize, r: usize) -> T::Monoid {
        self.propagate(k);
        if r <= a || b <= l {
            T::m0()
        } else if a <= l && r <= b {
            self.data[k]
        } else {
            T::f(
                self.do_query(a, b, 2 * k + 0, l, (l + r) >> 1),
                self.do_query(a, b, 2 * k + 1, (l + r) >> 1, r),
            )
        }
    }
    #[doc = "[l,r)"]
    pub fn query(&mut self, l: usize, r: usize) -> T::Monoid {
        let n = self.n;
        self.do_query(l, r, 1, 0, n)
    }
}

struct RUQ;
impl SEGLazyImpl for RUQ {
    type Monoid = i64;
    type OperatorMonoid = i64;
    fn m0() -> Self::Monoid {
        INF
    }
    fn om0() -> Self::OperatorMonoid {
        0
    }
    fn f(x: Self::Monoid, y: Self::Monoid) -> Self::Monoid {
        std::cmp::min(x, y)
    }
    fn g(x: Self::Monoid, y: Self::OperatorMonoid, _: usize) -> Self::Monoid {
        y
    }
    fn h(x: Self::OperatorMonoid, y: Self::OperatorMonoid) -> Self::OperatorMonoid {
        y
    }
}
// #[test]
// fn test_MAX_RUQ() {
//     let mut seg: SEGLazy<MAX_RUQ> = SEGLazy::new(10, MAX_RUQ::m0());
//     assert_eq!(seg.query(0, 3), 0);
//     seg.update(0, 2, 10); // [10,10,0,...]
//     assert_eq!(seg.query(0, 3), 10);
//     assert_eq!(seg.query(2, 3), 0);
//     seg.update(1, 5, 20);
//     assert_eq!(seg.query(0, 3), 20);
//     assert_eq!(seg.query(0, 1), 10);
//     seg.update(0, 1, 5);
//     assert_eq!(seg.query(0, 1), 5);
// }
fn solve() {
    let (n, q) = readuu();
    let mut seg: SEGLazy<RUQ> = SEGLazy::new(n, 100000000);
    let mut vp = vec![];
    for i in 0..q {
        let p = readuuu();
        vp.push((p.2, p.0 - 1, p.1));
    }

    vp.sort();
    for i in 0..q {
        let (x, l, r) = vp[i];
        seg.update(l, r, x as i64);
        let x = seg.query(0, n);
    }
    let mut flg = true;
    for i in 0..q {
        let (x, l, r) = vp[i];
        let x = x as i64;
        if x != seg.query(l, r) {
            flg = false;
        }
    }
    if !flg {
        println!("{:?}", -1);
        return;
    }
    let mut res = vec![0; n];
    for i in 0..n {
        res[i] = seg.query(i, i + 1);
    }
    for i in 0..res.len() {
        if (i != 0) {
            print!(" ");
        }
        print!("{}", res[i])
    }
    println!("");

    return;
}

fn main() {
    solve();
}