#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll MOD = 1000000000;
using P = pair<int,int>;
#define rep(i, n) for(int i = 0; i < n; i++)
#define all(x) (x).begin(),(x).end()

int main(){
    int n,q;
    bool B = false;
    cin >> n >> q;
    vector<vector<P>> x(n+1);
    vector<int> ans(n);
    rep(i,q){
        int l,r,b;
        cin >> l >> r >> b;
        l--;
        x[l].push_back(make_pair(b,1));
        x[r].push_back(make_pair(b,0));
    }
    map<int,pair<int,bool>> mp;
    rep(i,n){
        for(auto now : x[i]){
            int y,z;
            tie(y,z) = now;
            if(z){
                mp[y].first++;
                mp[y].second = false;
            }
            else{
                if(!mp[y].second) B = true;
                mp[y].first--;
            }
            if(!mp[y].first) mp.erase(y);
        }
        if(mp.size()){
            auto it = max_element(all(mp));
            ans[i] = (*it).first;
            (*it).second.second = true;
        }
        else ans[i] = MOD;
    }
    if(B) cout << -1;
    else rep(i,n) cout << ans[i] << " ";
    cout << endl;
    return 0;
}