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

class Main
{
    public static void main(String args[])throws Exception
    {
        BufferedReader bu=new BufferedReader(new InputStreamReader(System.in));
        StringBuilder sb=new StringBuilder();
        String s[]=bu.readLine().split(" ");
        int n=Integer.parseInt(s[0]),q=Integer.parseInt(s[1]);

        int a[][]=new int[q][3],i;
        Queue<int[]> g[]=new LinkedList[n];
        for(i=0;i<n;i++) g[i]=new LinkedList<>();
        for(i=0;i<q;i++)
        {
            s=bu.readLine().split(" ");
            for(int j=0;j<3;j++) a[i][j]=Integer.parseInt(s[j]);
            a[i][0]--;
            g[a[i][0]].add(new int[]{a[i][1],a[i][2]});
        }

        PriorityQueue<int[]> pq=new PriorityQueue<>(new Comparator<int[]>() {
            @Override
            public int compare(int[] o1, int[] o2) {
                if(o1[1]>o2[1]) return 1;
                else return -1;
            }});
        int ans[]=new int[n];
        for(i=0;i<n;i++)
        {
            while(!pq.isEmpty() && pq.peek()[0]<=i) pq.poll();
            while(!g[i].isEmpty()) pq.add(g[i].poll());
            if(!pq.isEmpty()) ans[i]=pq.poll()[1];
            else if(i>0) ans[i]=ans[i-1];
        }
        for(i=n-2;i>=0;i--)
        if(ans[i]==0) ans[i]=ans[i+1];

        st=new int[4*n];
        Arrays.fill(st,Integer.MAX_VALUE);
        for(i=0;i<n;i++) update(0,n-1,i,ans[i],0);

        boolean pos=true;
        for(i=0;i<q && pos;i++)
        pos&=query(0,n-1,a[i][0],a[i][1]-1,0)==a[i][2];
        if(pos)
        for(i=0;i<n;i++) sb.append(ans[i]+" ");
        else sb.append("-1");
        System.out.println(sb);
    }

    static int st[];
    static void update(int ss,int se,int i,int v,int n)
    {
        if(ss>se) return;
        if(ss==se)
        {
            st[n]=v;
            return;
        }

        int m=(se+ss)/2;
        if(i<=m) update(ss,m,i,v,2*n+1);
        else update(m+1,se,i,v,2*n+2);
        st[n]=Math.min(st[2*n+1],st[2*n+2]);
    }

    static int query(int ss,int se,int qs,int qe,int n)
    {
        if(ss>se || qe<ss || qs>se) return Integer.MAX_VALUE;
        if(qs<=ss && qe>=se) return st[n];

        int m=(se+ss)/2;
        return Math.min(query(ss,m,qs,qe,2*n+1),query(m+1,se,qs,qe,2*n+2));
    }
}