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[3],i;
        st=new int[4*n];
        Arrays.fill(st,Integer.MAX_VALUE);
        int ans[]=new int[n];
        TreeSet<Integer> ts=new TreeSet<>();
        for(i=0;i<n;i++)
        {
            ans[i]=(int)1e9;
            update(0,n-1,i,ans[i],0);
            ts.add(i);
        }

        PriorityQueue<int[]> pq=new PriorityQueue<>(new Comparator<int[]>() {
            @Override
            public int compare(int[] o1, int[] o2) {
                if(o1[2]<o2[2]) return 1;
                else return -1;
            }});
        for(i=0;i<q;i++)
        {
            s=bu.readLine().split(" ");
            for(int j=0;j<3;j++) a[j]=Integer.parseInt(s[j]);
            a[0]--; a[1]--;
            pq.add(new int[]{a[0],a[1],a[2]});
        }

        boolean pos=true;
        while(!pq.isEmpty() && pos)
        {
            a=pq.poll();
            Integer lo=ts.higher(a[0]-1);
            int qe=query(0,n-1,a[0],a[1],0);
            boolean can=qe==a[2];
            while(lo!=null)
            {
                int l=lo;
                if(l>a[1]) break;
                ts.remove(lo);
                can=true;
                ans[l]=a[2];
                update(0,n-1,l,a[2],0);
                lo=ts.higher(lo);
            }
            pos&=can;
        }

        if(pos)
        for(i=0;i<n;i++)
        {
            sb.append(ans[i]);
            if(i<n-1) sb.append(" ");
        }
        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));
    }
}