var
 x,y:array[1..100] of integer;
 b:array[1..100] of boolean;
 i,n,otv:integer; ex:boolean;
procedure reflesh;
    var
    i,max,col,j,yd:integer;
begin
   ex:=false;
   for i:=1 to n do
   if b[i] then
   begin
   col:=0;
   for j:=1 to n do
   if (i<>j) and b[j] then
   begin
   if (x[i]=y[i]) then break;
   if (x[i]<y[i]) then
   if ((x[j]>x[i]) and (y[i]>y[j])) then begin inc(col); yd:=j; end;
   if (x[i]>y[i]) then
   if ((x[i]>x[j]) and (y[i]<y[j])) then begin inc(col); yd:=j; end;
   end;
   if col=1 then begin  inc(otv); b[yd]:=false; ex:=true; break; end;
   end;
end;
begin
{   assign(input,'c:\test.txt');
   reset(input);}
   ex:=true;
   readln(n);
   fillchar(b,sizeof(b),true);
   for i:=1 to n do readln(x[i],y[i]);
   while ex do reflesh;
   writeln(otv);
end.

Try this
3
1 5
2 3
3 4
The right answer - 1.
You should use DP.

I am very weak in the theory.
My algorithm not true.
Whether you can give me idea. (my mail xxvictorxx@mail.ru (if has overlooked))

you algo wrong.

You need use DP.
i got AC O(N^2/2)

SURE?