#pragma region Macros
// #pragma GCC target("avx2")
#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
struct __INIT{__INIT(){cin.tie(0);ios::sync_with_stdio(false);cout<<fixed<<setprecision(15);}} __init;
#define rep(i, n) for (long long i = 0; i < (n); i++)
#define rrep(i, n) for (long long i = (n - 1); i >= 0; i--)
#define ALL(v) v.begin(), v.end()
#define endl "\n"
#define fi first
#define se second
#define popcount(bit) __builtin_popcount(bit)
#define popcountll(bit) __builtin_popcountll(bit)
#define pb push_back
#define eb emplace_back
using namespace atcoder;
using P = pair<int, int>;
using PP = pair<int, P>;
using PL = pair<long long, long long>;
using Graph = vector<vector<int>>;
typedef long long ll;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
const int fx[8] = {0, 1, 1, 1, 0, -1, -1, -1};
const int fy[8] = {1, 1, 0, -1, -1, -1, 0, 1};
template <typename T>
const auto INF = numeric_limits<T>::max()/2;

template<typename T>
struct RangeSet{
    set<pair<T,T>> st;
    T TINF;

    RangeSet(){
        TINF=(int)(1e9+ 1);
        st.emplace(TINF,TINF);
        st.emplace(-TINF,-TINF);
    }
    // [l,r] covered?
    bool covered(T l,T r){
        assert(l<=r);
        auto ite=prev(st.lower_bound({l+1,l+1}));
        return ite->first<=l and r<=ite->second;
    }
    bool covered(T x){
        return covered(x,x);
    }
    // [l, r]がカバーされているなら，その区間を返す. されていないなら[-TINF,-TINF]を返す
    pair<T,T> covered_by(T l,T r){
        assert(l<=r);
        auto ite=prev(st.lower_bound({l+1,l+1}));
        if(ite->first<=l and r<=ite->second) return *ite;
        return make_pair(-TINF,-TINF);
    }
    pair<T,T> covered_by(T x){
        return covered_by(x,x);
    }
    // insert[l,r], 増加量を返す
    T insert(T l,T r){
        assert(l<=r);
        auto ite=prev(st.lower_bound({l+1,l+1}));
        if(ite->first<=l and r<=ite->second) return T(0);
        T sum_erased=T(0);
        if(ite->first<=l and l<=ite->second+1){
            l=ite->first;
            sum_erased+=ite->second-ite->first+1;
            ite=st.erase(ite);
        }else ite=next(ite);
        while(r>ite->second){
            sum_erased+=ite->second-ite->first+1;
            ite=st.erase(ite);
        }
        if(ite->first-1<=r and r<=ite->second){
            sum_erased+=ite->second-ite->first+1;
            r=ite->second;
            st.erase(ite);
        }
        st.emplace(l,r);
        return r-l+1-sum_erased;
    }
    T insert(T x){
        return insert(x,x);
    }
    // erase [l,r], 減少量を返す
    T erase(T l,T r){
        assert(l<=r);
        auto ite=prev(st.lower_bound({l+1,l+1}));
        if(ite->first<=l and r<=ite->second){
            // 完全に1つの区間に包含されている
            if(ite->first<l)  st.emplace(ite->first,l-1);
            if(r<ite->second) st.emplace(r+1,ite->second);
            st.erase(ite);
            return r-l+1;
        }

        T ret=T(0);
        if(ite->first<=l and l<=ite->second){
            ret+=ite->second-l+1;// 消えた
            if(ite->first<l) st.emplace(ite->first,l-1);
            ite=st.erase(ite);// 次へ
        }else ite=next(ite);
        while(ite->second<=r){
            ret+=ite->second-ite->first+1;
            ite=st.erase(ite);
        }
        // 右端が区間の間にあるか
        if(ite->first<=r and r<=ite->second){
            ret+=r-ite->first+1;
            if(r<ite->second) st.emplace(r+1,ite->second);
            st.erase(ite);
        }
        return ret;
    }
    T erase(T x){
        return erase(x,x);
    }
    // number of range
    int size(){
        return (int)st.size()-2;
    }
    // mex [x,~)
    T mex(T x=0){
        auto ite=prev(st.lower_bound({x+1,x+1}));
        if(ite->first<=x and x<=ite->second) return ite->second+1;
        else return x;
    }
    void output(){
        cout<<"RangeSet : ";
        for(auto &p:st){
            if(p.first==-TINF or p.second==TINF) continue;
            cout<<"["<<p.first<<", "<<p.second<<"] ";
        }
        cout<<"\n";
    }
};


using S = int;
using F = int;
S op(S a, S b) { return min(a, b); }
S e() { return int(1e9); }
S mapping(F x, S a) { return x == -1 ? a : x; }
F composition(F f, F g) { return f == -1 ? g : f; }
F id() { return -1; }

int main() {
  int n, q;
  cin >> n >> q;
  vector<array<int, 3>> query(q);
  rep(i, q) {
    int l, r, b;
    cin >> l >> r >> b;
    l--;
    query[i] = {b, l, r};
  }
  sort(ALL(query));
  lazy_segtree<S, op, e, F, mapping, composition, id> seg(n);

  for (auto [b, l, r] : query) seg.apply(l, r, b);
  for (auto [b, l, r] : query) {
    if (seg.prod(l, r) != b) {
      cout << -1 << "\n";
      return 0;
    }
  }
  rep(i, n) cout << seg.get(i) << (i + 1 == n ? "\n" : " ");
}