// 解法2 (愚直)
#include <bits/stdc++.h>
using namespace std;

static const int INF = 2e9;

// Segment-Tree
struct SegmentTree {
  int n;
  vector<int> dat;
  
  SegmentTree(int _n) {
    init(_n);
  }
  
  SegmentTree(vector<int> &a) {
    init((int) a.size());
    for (int i = 0; i < a.size(); i++) dat[i + n - 1] = a.at(i);
    for (int i = n - 2; i >= 0; i--) dat[i] = min(dat[2 * i + 1], dat[2 * i + 2]);
  }
  
  void init(int _n) {
    n = 1;
    while (n < _n) n *= 2;
    dat.assign(2 * n - 1, INF);
  }
  
  // [a, b)の値. ノードkの範囲は[l, r)
  int query(int a, int b, int k = 0, int l = 0, int r = -1) {
    if (r == -1) r = n;
    if (r <= a || b <= l) return INF;
    if (a <= l && r <= b) return dat[k];
    else {
      int vl = query(a, b, 2 * k + 1, l, (l + r) / 2);
      int vr = query(a, b, 2 * k + 2, (l + r) / 2, r);
      return min(vl, vr);
    }
  }
};

int main() {
  int n, q;
  cin >> n >> q;
  
  vector<vector<int>> query(q, vector<int>(3));
  for (int i = 0; i < q; i++) {
    cin >> query.at(i).at(1) >> query.at(i).at(2) >> query.at(i).at(0);
    query.at(i).at(1)--;
    query.at(i).at(2)--;
  }
  
  sort(query.begin(), query.end());
  
  vector<int> a(n, 2e9);
  for (int i = 0; i < q; i++) {
    for (int j = query.at(i).at(1); j <= query.at(i).at(2); j++) {
      a.at(j) = query.at(i).at(0);
    }
  }
  
  SegmentTree st(a);
  
  bool ok = true;
  for (int i = 0; i < q; i++) {
    if (st.query(query.at(i).at(1), query.at(i).at(2) + 1) != query.at(i).at(0)) {
      ok = false;
    }
  }
  
  if (ok) {
    for (int i = 0; i < n; i++) {
      if (i) cout << " ";
      cout << min<int>(st.query(i, i + 1), 1e9);
    }
    cout << '\n';
  }
  else {
    cout << -1 << '\n';
  }
}