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

struct iofast_t {
    iofast_t() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} iofast;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return std::vector(arg, init);
    else return std::vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

template <typename T, typename Compare = less<T>>
T &chmin(T &l, T r, Compare &&f = less<T>()) { return l = min(l, r, f); }
template <typename T, typename Compare = less<T>>
T &chmax(T &l, T r, Compare &&f = less<T>()) { return l = max(l, r, f); }

#include <atcoder/segtree>

constexpr int inf = INT_MAX / 2;

int op(int x, int y) {
    return min(x, y);
}

int elem() {
    return inf;
}

using segtree = atcoder::segtree<int, op, elem>;

int main() {
    int n, q; cin >> n >> q;
    auto query = vec<tuple<int, int, int>>(uns, q);
    for (auto &[l, r, b] : query) {
        cin >> l >> r >> b; --l;
    }

    sort(rbegin(query), rend(query), [](auto x, auto y) {
        return get<2>(x) < get<2>(y);
    });

    auto a = vec<int>(1, n);

    set<int> rem;
    for (int i = 0; i < n; ++i) {
        rem.insert(i);
    }

    for (auto [l, r, b] : query) {
        auto iter = rem.lower_bound(l);
        auto last = rem.lower_bound(r);

        while (iter != last) {
            a[*iter] = b;
            iter = rem.erase(iter);
        }
    }

    segtree seg(a);
    for (auto [l, r, b] : query) {
        if (seg.prod(l, r) != b) {
            cout << -1 << endl;
            return 0;
        }
    }

    cout << a[0];
    for (int i = 1; i < n; ++i) {
        cout << ' ' << a[i];
    }
    cout << endl;
}