program heavymetal;
var f,g:text;
    n,a,b,ok,j,s,i:longint;
    v:array[1..1000000000]of 0..1;
begin
assign(f,'heavymetal.in');
assign(g,'heavymetal.out');
reset(f);
rewrite(g);
read(f,n);
for i:=1 to n do
  begin
    read(f,a,b);
    ok:=0;
    for j:=a to b do
      if (v[j]=1)then
        begin
          ok:=1;
          break;
        end;
    if (ok=0)then
      begin
        s:=s+(b-a);
        for j:=a+1 to b-1 do
          v[j]:=1;
      end;
  end;
write(g,s);
close(f);
close(g);
end.