program concurs;
var f,g:text;
   i,csere2,l,csere,p,min,hej,max,hany,o,k,db:integer;
   e,uje:array[1..1000] of integer;
   j,ujj:array[1..50] of integer;
   s:array[1..50] of integer;
   n:array[1..50] of byte;
   begin
   assign(f,'concurs.in');
   assign(g,'concurs.out');
   reset(f);
   rewrite(g);
   readln(f,p);
   while not eof(f) do
   begin
   db:=db+1;
   read(f,j[db],e[db]);
   readln(f);
   end;
   for i:=1 to p do
   if s[j[i]] = 0 then
   s[j[i]]:=1;
   for i:=1 to 50 do
   if s[i]=1 then
   o:=o+1;
   writeln(g,o);
   db:=1;
   for i:=1 to 50 do
     begin
     if j[i] <>0 then
     begin
       for k:=1 to 50 do
       begin
         if j[i]=k then
         n[k]:=n[k]+1;
       end;
      db:=db+1;
     end;
     end;
   for i:=1 to 50 do
   if n[i]<>0 then
   write(g,n[i],' ');
   writeln(g);
   min:=maxint;
   for k:=1 to p do
   begin
     for i:=1 to p do
       begin
        if e[i]<min then
         begin
           min:=e[i];
           hej:=i;
         end;
        end;
   ujj[k]:=j[hej];
   uje[k]:=e[hej];
   min:=maxint;
   e[hej]:=maxint;
   j[hej]:=maxint;
   end;
   for i:=1 to p-1 do
   begin
   if (ujj[i] = uje[i+1]) or (ujj[i] = ujj[i-1]) then
   begin
   csere:=ujj[i];
   ujj[i]:=ujj[i+1];
   ujj[i+1]:=csere;
   csere2:=uje[i];
   uje[i]:=uje[i+1];
   uje[i+1]:=csere2;
   end;
   end;
   for i:=1 to p do
   writeln(g,ujj[i],' ',uje[i]);
   close(g);
   end.