program EmberAsh;
var
a:array[0..10000000]of longint;
b:array[0..10000000]of boolean;
i,j,k,t1,t2,n,m,min,max:longint;
fin,fout:text;

BEGIN
assign(fin,'punch.in');reset(fin);
assign(fout,'punch.out');rewrite(fout);
readln(fin,n);
min:=maxlongint;max:=0;
for i:=1 to n do
  begin
  inc(k);
  readln(fin,t1,t2);
  if t1<min then min:=t1;
  if t2>max then max:=t2;
  for j:=t1 to t2 do
    a[j]:=k;
  end;
for i:=min to max do
  if b[a[i]]=false then
    begin
    inc(m);
    b[a[i]]:=true;
    end;
writeln(fout,m);
close(fin);close(fout);
END.