program heavymetal;
{$APPTYPE CONSOLE}
uses
  SysUtils;
type nr = record
a,b:longint;
end;
var c,i,j,n,m:longint;
    fin,fout:text;
    v:array [1..100000] of nr;
{*----------------------------*}
function cauta:boolean;
begin
        cauta:=true;
        for j:=1 to i-1 do
                if j<>i then
                begin
                        if ((v[i].a>=v[j].a) and (v[i].b<=v[j].b)) then
                        begin
                                cauta:=false;
                                exit;
                        end;
                end;
end;
{*-----------MAIN-------------*}
begin
        assign(fin,'heavymetal.in'); reset(fin);
        assign(fout,'heavymetal.out'); rewrite(fout);
        readln(fin,n);
        for i:=1 to n do readln(fin,v[i].a,v[i].b);
        c:=0;
        for i:=1 to n do
        begin
                if cauta then c:=c+v[i].b-v[i].a;
        end;
        writeln(fout,c);
        close(fin);
        close(fout);
end.