import java.io.*;
import java.util.*;

public class Main {
    static final int MAX = 1000000000;
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int q = sc.nextInt();
        int[] ans = new int[n];
        TreeSet<Integer> remain = new TreeSet<>();
        for (int i = 0; i < n; i++) {
            remain.add(i);
        }
        HashMap<Integer, TreeSet<Integer>> used = new HashMap<>();
        Query[] queries = new Query[q];
        for (int i = 0; i < q; i++) {
            queries[i] = new Query(sc.nextInt() - 1, sc.nextInt() - 1, sc.nextInt());
        }
        Arrays.sort(queries);
        for (Query x : queries) {
            Integer key = x.left;
            while ((key = remain.ceiling(key)) != null) {
                if (key > x.right) {
                    break;
                }
                if (!used.containsKey(x.value)) {
                    used.put(x.value, new TreeSet<>());
                }
                used.get(x.value).add(key);
                ans[key] = x.value;
                remain.remove(key);
            }
            if (!used.containsKey(x.value)) {
                System.out.println(-1);
                return;
            }
            Integer next = used.get(x.value).ceiling(x.left);
            if (next == null || next > x.right) {
                System.out.println(-1);
                return;
            }
        }
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < n; i++) {
            if (i > 0) {
                sb.append(" ");
            }
            if (ans[i] == 0) {
                ans[i] = MAX;
            }
            sb.append(ans[i]);
        }
        System.out.println(sb);
    }
    
    static class Query implements Comparable<Query> {
        int left;
        int right;
        int value;
        
        public Query(int left, int right, int value) {
            this.left = left;
            this.right = right;
            this.value = value;
        }
        
        public int compareTo(Query another) {
            return another.value - value;
        }
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public String nextLine() throws Exception {
        return br.readLine();
    }
    
    public String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}