#include <bits/stdc++.h>
using namespace std;

int inf = 1000000000;

template <typename T>
struct SegmentTree {
    int n;
    vector<T> dat;
    SegmentTree() {}
    SegmentTree(int N) {
        n = 1;
        while(n < N) {
            n *= 2;
        }
        dat.resize(2*n-1,inf);
    }
    void update(int x, T val) {
        x += (n-1);
        dat[x] = val;
        while(x > 0) {
            x = (x-1)/2;
            dat[x] = min(dat[2*x+1],dat[2*x+2]);
        }
    }
    T query(int a, int b, int k, int l, int r) {
        if(r <= a || b <= l) return inf;
        if(a <= l && r <= b) return dat[k];
        T vl = query(a, b, 2*k+1, l, (l+r)/2);
        T vr = query(a, b, 2*k+2, (l+r)/2, r);
        return min(vl, vr);
    }
    T query(int a,int b) {//[a,b)
        return query(a,b,0,0,n);
    }
};

int main() {
    int N,Q;
    cin >> N >> Q;
    vector<array<int,3>>tmp(Q);
    for(int i = 0; i < Q; i++) {
        cin >> tmp[i][1] >> tmp[i][2] >> tmp[i][0];
        tmp[i][1]--;
        tmp[i][2]--;
    }
    sort(tmp.rbegin(),tmp.rend());
    set<int>st;
    for(int i = 0; i < N; i++) {
        st.insert(i);
    }
    vector<int>ans(N,inf);
    SegmentTree<int>Seg(N);
    for(int i = 0; i < Q; i++) {
        while (st.lower_bound(tmp[i][1]) != st.end() && *st.lower_bound(tmp[i][1]) <= tmp[i][2]) {
            ans[*st.lower_bound(tmp[i][1])] = tmp[i][0];
            Seg.update(*st.lower_bound(tmp[i][1]),tmp[i][0]);
            st.erase(st.lower_bound(tmp[i][1]));
        }
        if(Seg.query(tmp[i][1],tmp[i][2]+1) != tmp[i][0]) {
            cout << -1 << endl;
            return 0;
        }
    }
    for(int i = 0; i < N; i++) {
        cout << ans[i] << ((i+1 == N)?"\n":" ");
    }
}