#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int INF = 1000000100;
const ll INFL = 2e18;
template <class T>bool chmin(T &a, T b){ if (a > b) { a = b; return true;} else return false;}
template <class T>bool chmax(T &a, T b){ if (a < b) { a = b; return true;} else return false;}

using P = pair<int,int>;

int main() {
    int N,Q;
    cin >> N >> Q;

    vector<int> ans(N,INF);    

    multiset<int> st;
    vector<vector<P>> query(N);
    priority_queue<P, vector<P>, greater<P>> pq;
    for (int i = 0;i < Q;i++) {
        int l, r, B;
        cin >> l >> r >> B;
        l--, r--;
        query[l].push_back({r, B});
    }

    int rem = Q;
    map<int,int> mp;
    
    for (int i = 0;i < N;i++) {
        for (int j = 0;j < query[i].size();j++) {
            int r, B;
            tie(r, B) = query[i][j];
            st.insert(B);
            pq.push({r, B});
            mp[B]++;
        }
        if (st.size()) {
            ans[i] = *st.rbegin();
            rem -= mp[*st.rbegin()];
            mp[*st.rbegin()] = 0;
        }

        while (pq.size() && i == pq.top().first) {
            int r,B;
            tie(r, B) = pq.top();
            pq.pop();
            st.erase(st.find(B));
        }
    }

    if (rem) {
        cout << -1 << endl;
    }
    else {
        for (int i = 0;i < N;i++) {
            if (i != N-1)cout << ans[i] << " ";
            else cout << ans[i] << endl;
        }
    }
}