program Bus;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var Data: array[0..6000] of Cardinal;
		F: Text; I: Integer; N: Cardinal;
    Timeline: array[1..100000] of Cardinal;
    Peaks: Cardinal;
    Peak: array[1..6000] of Cardinal;
    ActN: Cardinal;

procedure ResetTimeline();
var I: Integer;
begin
for I:=1 to 100000 do
Timeline[I]:=0;
end;

procedure CalcTimeline();
var I,J: Integer;
begin
for J:=0 to (N-1) do
if Data[J*2]<>0 then
for I:=Data[J*2] to Data[J*2+1] do
Inc(Timeline[I]);
end;

procedure Del(P: Cardinal);
begin
Dec(ActN);
Data[P*2]:=0;
end;

procedure Sub(P: Cardinal);
var I: Integer;
begin
for I:=0 to (N-1) do
if ((Data[I*2]<=P)and(Data[I*2+1]>=P)) then
Del(I);
end;

procedure Add(P: Cardinal);
begin
Inc(Peaks);
Peak[Peaks]:=P;
Sub(P);
end;

procedure ProcessTimeline();
var Pn, Pv: Cardinal;
		I: Integer;
begin
Pn:=0; Pv:=0;
for I:=1 to 100000 do
if (Timeline[I]>Pv) then
begin Pv:=Timeline[I]; Pn:=I; end;
Add(Pn);
end;

begin
Peaks:=0;
Assign(F,'Bus.dat'); Reset(F);
ReadLn(F,N); ActN:=N;
for I := 0 to (N-1) do
ReadLn(F,Data[I*2],Data[I*2+1]);
Close(F);
while (ActN>0) do
begin
ResetTimeline;
CalcTimeline;
ProcessTimeline;
end;
Assign(F,'Bus.sol'); Rewrite(F);
WriteLn(F,Peaks);
for I:=1 to Peaks do
WriteLn(F,Peak[I],' ',Peak[I]+1);
Close(F);
end.