#include <iostream>
#include <map>
#include <vector>
#include <algorithm>
#include <numeric>
#include <cassert>
#include <cmath>
#include <queue>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <functional>

#define rep(i,n,s) for(int i = (s); i < int(n); i++)
#define MM << " " << 
#define all(x) x.begin(), x.end()

template<class T>
using MinHeap = std::priority_queue<T, std::vector<T>, std::greater<T>>;

using ll = long long;
using Pii = std::pair<int, int>;
using Pll = std::pair<ll, ll>;

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

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

template<class T>
void vdeb(std::vector<T> &da) {
    auto n = da.size();
    for(size_t i = 0; i < n; i++) {
        if(i == n-1) std::cout << da[i] << std::endl;
        else std::cout << da[i] << " ";
    }
}
template<>
void vdeb(std::vector<std::string> &da) {
    auto n = da.size();
    for(size_t i = 0; i < n; i++) {
        std::cout << da[i] << std::endl;
    }
}


template<typename T>
struct SegTree{
    std::vector<T> nod;
    T t0;
    std::function<T(T,T)> operation;
    std::function<T(T,T)> merge;
    int size;
    SegTree(int _size, T _t0, std::function<T(T,T)> _operation, std::function<T(T,T)> _merge):t0(_t0), operation(_operation), merge(_merge){
        size=1;
        while(_size>size){
            size*=2;
        }
        nod=std::vector<T>(size*2-1, t0);
    }
    void update(int k, T a){ // operation(da[k], a)
        assert(0<= k && k < size);
        k+=size-1;
        nod[k] = operation(nod[k], a);
        while(k>0){
            k=(k-1)/2;
            nod[k] = merge(nod[k*2+1], nod[k*2+2]); 
        }
    }
    void range_update(int a, int b, T x) {
        assert(0 <= a && a < size);
        assert(0 <= b && b <= size);
        assert(a <= b);
        range_update_query(a, b, 0, 0, size, x);
    }
    T sum(int a, int b) { // merge[a, b)
        assert(0 <= a && a < size);
        assert(0 <= b && b <= size);
        assert(a <= b);
        return sum_query(a, b, 0, 0, size);
    }
    void deb(){
        for(int i=0;i<size*2-1;i++){
            if(i==size*2-2) std::cout << nod[i] <<std:: endl;
            else std::cout << nod[i] << ' ';
        }
        return;
    }
    private:
    void range_update_query(int a,int b,int k,int l,int r,T x){
        if(r<=a||b<=l){
            return;
        }
        if(a<=l && r<=b){
            nod[k] = operation(nod[k], x);
            return;
        }
        else{
            range_update_query(a,b,k*2+1,l,(l+r)/2,x);
            range_update_query(a,b,k*2+2,(l+r)/2,r,x);
            return;
        }
    }
    T sum_query(int a,int b,int k,int l,int r){
        if(r<=a||b<=l){
            return t0;
        }
        if(a<=l && r<=b){
            return nod[k];
        }
        else{
            return merge(sum_query(a,b,k*2+1,l,(l+r)/2),sum_query(a,b,k*2+2,(l+r)/2,r));
        }
    }
};

using namespace std;

int main() {
    int n, q; cin >> n >> q;
    vector<vector<Pii>> da(n+1);
    vector<pair<Pii, int>> query(q);
    rep(i,q,0) {
        int l, r, b; cin >> l >> r >> b;
        da[l-1].push_back({b, 0});
        da[r].push_back({b, 1});
        query[i] = {{l-1, r}, b};
    }
    SegTree<int> st(n, 1000000000, [](int x, int y){return min(x, y);}, [](int x, int y){return min(x, y);});
    map<int, int> mp;
    rep(i,n,0) {
        for(auto &j : da[i]) {
            if(j.second) {
                mp[j.first]--;
                if(mp[j.first] == 0) mp.erase(j.first);
            } else {
                mp[j.first]++;
            }
        }
        if(!mp.empty()) st.update(i, (--mp.end())->first);
    }
    rep(i,q,0) {
        if(st.sum(query[i].first.first, query[i].first.second) != query[i].second) {
            cout << -1 << endl;
            return 0;
        }
    }
    vector<int> ans(n);
    rep(i,n,0) ans[i] = st.sum(i, i+1);
    vdeb(ans);
}