#include <bits/stdc++.h>
#include <boost/multiprecision/cpp_int.hpp>
#include <boost/multiprecision/cpp_dec_float.hpp>

using namespace std;
using namespace boost::multiprecision;

typedef cpp_int BigInt;
typedef cpp_dec_float_100 PreciseFloat;

#define int long long
#define rep(i, n) for(int (i)=0;(i)<(n);(i)++)
#define rrep(i, n) for(int (i)=((n)-1);(i)>=0;(i)--)
#define itn int
#define miele(v) min_element(v.begin(), v.end())
#define maele(v) max_element(v.begin(), v.end())
#define SUM(v) accumulate(v.begin(), v.end(), 0LL)
#define lb(a, key) lower_bound(a.begin(),a.end(),key)
#define ub(a, key) upper_bound(a.begin(),a.end(),key)
#define COUNT(a, key) count(a.begin(), a.end(), key)
#define BITCOUNT(x) __builtin_popcount(x)
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define F first
#define S second
using P = pair<int, int>;
using WeightedGraph = vector<vector<P>>;
using UnWeightedGraph = vector<vector<int>>;
using Real = long double;
using Point = complex<Real>; //Point and Vector2d is the same!
// p.real() or real(p) -> x軸, p.imag() or imag(p) -> y軸
using Vector2d = complex<Real>;
const int MOD = 1000000007;
const long long INF = 1LL << 60;
const double EPS = 1e-15;
const double PI = 3.14159265358979323846;

template<typename T>
int getIndexOfLowerBound(vector<T> &v, T x) {
    return lower_bound(v.begin(), v.end(), x) - v.begin();
}

template<typename T>
int getIndexOfUpperBound(vector<T> &v, T x) {
    return upper_bound(v.begin(), v.end(), x) - v.begin();
}

template<class T>
inline bool chmin(T &a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
inline bool chmax(T &a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)

istream &operator>>(istream &is, Point &p) {
    Real a, b;
    is >> a >> b;
    p = Point(a, b);
    return is;
}

template<typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &p_var) {
    is >> p_var.first >> p_var.second;
    return is;
}

template<typename T>
istream &operator>>(istream &is, vector<T> &vec) {
    for (T &x : vec) is >> x;
    return is;
}

template<typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
    os << pair_var.first << ' ' << pair_var.second;
    return os;
}

template<typename T>
ostream &operator<<(ostream &os, vector<T> &vec) {
    for (int i = 0; i < vec.size(); i++)
        os << vec[i] << ' ';
    return os;
}

template<typename T, typename U>
ostream &operator<<(ostream &os, vector<pair<T, U>> &vec) {
    for (int i = 0; i < vec.size(); i++)
        os << vec[i] << '\n';
    return os;
}

template<typename T>
ostream &operator<<(ostream &os, vector<vector<T>> &df) {
    for (auto &vec : df) os << vec;
    return os;
}

template<typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
    repi(itr, map_var) {
        os << *itr << ' ';
        itr++;
        itr--;
    }
    return os;
}

template<typename T>
ostream &operator<<(ostream &os, set<T> &set_var) {
    repi(itr, set_var) {
        os << *itr << ' ';
        itr++;
        itr--;
    }
    return os;
}

void print() { cout << endl; }

template<class Head, class... Tail>
void print(Head &&head, Tail &&... tail) {
    cout << head;
    if (sizeof...(tail) != 0) cout << " ";
    print(forward<Tail>(tail)...);
}

struct LazySegTree{ // add and min
    int n;
    vector <pair<int, int>> node, lazy;

    LazySegTree(vector <int> v){
        int sz = v.size();
        n = 1;
        while(n<sz) n*=2;
        node.resize(2*n-1, {INF, INF});
        lazy.resize(2*n-1);
        for(int i=0; i<sz; i++) node[i+n-1] = {v[i], i}; //一番下側
        for(int i=n-2;i>=0;i--) node[i] = min(node[i * 2 + 1], node[i * 2 + 2]);
    }

    void eval(int k,int l, int r){
        if(lazy[k].F != 0){
            node[k].F += lazy[k].F;
            if(r - l >1){
                lazy[2*k+1].F += lazy[k].F;
                lazy[2*k+2].F += lazy[k].F;
            }
            lazy[k] = {0, 0};
        }
    }


    void add(int a, int b, int x, int k=0, int l=0, int r=-1) {

        if(r < 0) r = n;
        eval(k, l, r);
        if(b <= l || r <= a) return;
        if(a <= l && r <= b) {
            lazy[k].F += x;
            eval(k, l, r);
        }
        else {
            add(a, b, x, 2*k+1, l, (l+r)/2);
            add(a, b, x, 2*k+2, (l+r)/2, r);
            //chmin(node[k], min(node[2*k+1],node[2*k+2]));
            node[k] = min(node[k * 2 + 1], node[k * 2 + 2]);
        }
    }

    pair<int, int> getmin(int a, int b, int k=0, int l=0, int r=-1) {
        if(r < 0) r = n;
        if(b <= l || r <= a) return {INF, INF};
        eval(k, l, r);
        if(a <= l && r <= b) return node[k];
        pair<int, int> vl = getmin(a, b, 2*k+1, l, (l+r)/2);
        pair<int, int> vr = getmin(a, b, 2*k+2, (l+r)/2, r);
        return min(vl, vr);
    }
};

void koushin(queue<pair<int, int>> &q, LazySegTree &seg) {
    while(!q.empty()) {
        pair<int, int> p = q.front();
        q.pop();
        seg.add(p.F, p.S+1, 1);
    }
}

signed main(void) { cin.tie(0); ios::sync_with_stdio(false);
    int n; cin>>n;
    int q; cin>>q;

    vector <tuple<int,int,int>> query(q);

    vector<int> tmp(214514);
    LazySegTree seg(tmp);

    rep(i, q) {
        int l, r, b; cin>>l>>r>>b;
        l--, r--;
        query[i] = {b, l, r};
    }

    sort(query.begin(),query.end(),greater<>());
    queue <pair<int, int>> que;

    vector<int> ans(n);

    for (int i = 0; i < query.size(); ++i) {
        int l = get <1>(query[i]), r = get <2>(query[i]), b = get <0>(query[i]);
        auto mie = seg.getmin(l, r+1);
        if(mie.F == 0) {
            ans[mie.S] = b;
        } else {
            cout << -1 << '\n';
            return 0;
        }
        que.push({l, r});

        if(i + 1 < query.size() && get<0>(query[i+1]) == b) continue;
        else {
            koushin(que, seg);
        }
    }

    rep(i, n) {
        if(ans[i] == 0) {
            ans[i] = 1e9;
        }
    }

    rep(i, n) {
        cout << ans[i];
        if(i != n-1) {
            cout << ' ';
        } else {
            cout << '\n';
        }
    }
}