my source:
type TOtr = record
                  l: longint;
                  r: longint;
            end;
var  M,j: longint;
     Otr: TOtr;
     Buf: TOtr;
     Res: array[1..100000] of TOtr;
     i:   longint;
function IsOtr(o1,o2: TOtr): boolean; {o1 in o2}
begin
     isotr:=(o1.l>=o2.l) and (o1.l<=o2.r) and (o1.r<=o2.r) and (o1.r>=o2.l);
end;
procedure Sort(var o: TOtr);
var i: longint;
begin
     if o.l>o.r then
        begin
             i:=o.l;
             o.l:=o.r;
             o.r:=i;
        end;
end;
begin
     readln(m);
     Buf.l:=0;
     Buf.r:=m;
     readln(otr.l,otr.r);
     j:=0;
     if otr.l>otr.r then sort(otr);
     repeat
           if isotr(otr,buf) then
              begin
                   inc(j);
                   res[j]:=otr;
              end;
           readln(otr.l,otr.r);
     until (otr.l=0) and (otr.r=0);
     if j > 0 then
        begin
             writeln(j);
             for i:=1 to j do
                 writeln(res[i].l,' ',res[i].r);
        end
     else
         writeln('No solution');
end.
i get WA on 3rd test.
but why?

procedure sort; - wrong
3
0 1
2 3
1 2
0 0
:( wrong answer