program heavy;
type vect = record
          x,y : longint;
          end;
var A : array [1..100000] of vect;
    B : vect;
    n,i,S,m : longint;
    ok : boolean;
    f : text;
begin
assign(f,'heavymetal.in');
reset(f);
readln(f,n);
for i := 1 to n do
readln(f,A[i].x,A[i].y);
close(f);

repeat
ok := true;
for i := 1 to n-1 do
if A[i].y<A[i+1].y then begin
                        B := A[i];
                        A[i] := A[i+1];
                        A[i+1] := B;
                        ok := false;
                        end;
until ok;


repeat
ok := true;
for i := 1 to n-1 do
if A[i].x>A[i+1].x then begin
                        B := A[i];
                        A[i] := A[i+1];
                        A[i+1] := B;
                        ok := false;
                        end;
until ok;

S := A[1].y-A[1].x;
m := A[1].y;


for i := 2 to n do
if A[i].x>=m then begin
                  m := A[i].y;
                  S := S+A[i].y-A[i].x;
                  end;


assign(f,'heavymetal.out');
rewrite(f);
write(f,S);
close(f);

end.