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

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int q = sc.nextInt();
        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);
        TreeSet<Integer> all = new TreeSet<>();
        for (int i = 0; i < n; i++) {
            all.add(i);
        }
        int[] ans = new int[n];
        Arrays.fill(ans, 1000000000);
        TreeSet<Integer> store = new TreeSet<>();
        int prev = Integer.MAX_VALUE;
        for (Query x : queries) {
            if (prev != x.value) {
                store.clear();
            }
            Integer key = store.floor(x.right);
            boolean enable = (key != null && key >= x.left);
            ArrayList<Integer> list = new ArrayList<>();
            key = x.left - 1;
            while ((key = all.higher(key)) != null) {
                if (key > x.right) {
                    break;
                }
                all.remove(key);
                list.add(key);
            }
            if (!enable && list.size() == 0) {
                System.out.println(-1);
                return;
            }
            for (int y : list) {
                ans[y] = x.value;
                store.add(y);
            }
            prev = x.value;
        }
        System.out.println(String.join(" ", Arrays.stream(ans).mapToObj(String::valueOf).toArray(String[]::new)));
    }
    
    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 Utilities {
    static String arrayToLineString(Object[] arr) {
        return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n"));
    }
    
    static String arrayToLineString(int[] arr) {
        return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new));
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public int[] nextIntArray() throws Exception {
        return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}