Input

  1 type
  2   arr=record
  3     x,y,l,r:longint;
  4   end;
  5 var
  6   n,m,tk,ans,ll:longint;
  7   a:array [0..3001] of arr;
  8   fa:array [0..1001] of longint;
  9 function max(o,p:longint):longint;
 10 begin
 11   if o>p then exit(o);
 12   exit(p);
 13 end;
 14
 15 procedure init;
 16 var
 17   i:longint;
 18 begin
 19   readln(n,m);
 20   tk:=0;
 21   for i:=1 to m do
 22     begin
 23       readln(a[i].x,a[i].y,a[i].l,a[i].r);
 24       tk:=max(tk,a[i].r);
 25     end;
 26 end;
 27
 28 procedure qsort(l,r:longint);
 29 var
 30   i,j,mid:longint;
 31   t:arr;
 32 begin
 33   if l>r then exit;
 34   i:=l; j:=r;
 35   mid:=a[(l+r) div 2].r;
 36   repeat
 37     while a[i].r<mid do inc(i);
 38     while a[j].r>mid do dec(j);
 39     if i<=j then
 40       begin
 41         t:=a[i]; a[i]:=a[j]; a[j]:=t;
 42         inc(i); dec(j);
 43       end;
 44   until i>j;
 45   qsort(i,r);
 46   qsort(l,j);
 47 end;
 48
 49 function get(x:longint):longint;
 50 begin
 51   if (fa[x]=0) or (fa[x]=x) then exit(x);
 52   fa[x]:=get(fa[x]);
 53   exit(fa[x]);
 54 end;
 55
 56 function fd(l,r:longint):boolean;
 57 var
 58   i,x,y:longint;
 59 begin
 60   fillchar(fa,sizeof(fa),0);
 61   for i:=1 to m do
 62     if (a[i].l<=l) and (a[i].r>=r) then
 63       begin
 64         x:=get(a[i].x); y:=get(a[i].y);
 65         fa[x]:=y;
 66       end;
 67   if get(1)=get(n) then exit(true);
 68   exit(false);
 69 end;
 70
 71 procedure main;
 72 var
 73   i,r,l,mid,t:longint;
 74 begin
 75   ans:=0;
 76   for i:=1 to m do
 77     begin
 78       l:=1; r:=tk;
 79       while l+1<r do
 80         begin
 81           mid:=(l+r) div 2;
 82           if fd(a[i].l,mid) then l:=mid
 83                             else r:=mid;
 84         end;
 85       if not fd(a[i].l,r) then r:=l;
 86       t:=r-a[i].l+1;
 87       if (t>ans) or (t=ans) and (a[i].l<ll) then
 88         begin
 89           ans:=t; ll:=a[i].l;
 90         end;
 91     end;
 92 end;
 93
 94 procedure print;
 95 var
 96   i,rr:longint;
 97 begin
 98   writeln(ans);
 99   rr:=ans+ll-1;
100   for i:=ll to rr do
101     write(i,' ');
102 end;
103
104 begin
105   init;
106   qsort(1,m);
107   main;
108   print;
109 end.