{$R-}
type nd=^nod;
     nod=record
          val:word;
          next:nd
         end;
var f:text;
    j,x,y,n,c,i:word;
    k:longint;
    l,r:array[1..10000]of word;
    ver:array[1..10000]of boolean;
    p:nd;
    g:array[1..10000]of nd;

function pairup(x:word):boolean;
var p:nd;
begin
if not ver[x]then
 begin
  ver[x]:=true;
  p:=g[x];
  while p<>nil do
   begin
    if r[p^.val]=0 then
     begin
      l[x]:=p^.val;
      r[p^.val]:=x;
      pairup:=true;
      exit;
     end;
    p:=p^.next
   end;
  p:=g[x];
  while p<>nil do
   begin
    if pairup(r[p^.val])then
     begin
      l[x]:=p^.val;
      r[p^.val]:=x;
      pairup:=true;
      exit
     end;
    p:=p^.next
   end;
  pairup:=false
 end
             else
 pairup:=false;
end;

begin
assign(f,'cuplaj.in');
reset(f);
read(f,n,m,k);
for i:=1 to k do
 begin
  read(f,x,y);
  if (x<>0)and(y<>0)then
   begin
    new(p);
    p^.val:=y;
    p^.next:=g[x];
    g[x]:=p;
   end;
 end;
close(f); c:=0;
for i:=1 to n do
 if l[i]=0 then
  begin
   for j:=1 to n do
    ver[j]:=false;
   if pairup(i) then
    inc(c);
  end;
assign(f,'cuplaj.out');
rewrite(f);
writeln(f,c);
for i:=1 to n do
 if l[i]<>0 then
  writeln(f,i,' ',l[i]);
close(f);
end.