program bing;
var
 f1,f2:text;
 n:integer;
 a,b,s:array[1..10000] of longint;
 z:array[1..100000000] of longint;
 m:longint;
procedure init;
var
 i,j:longint;
begin
 assign(f1,'punch.in');reset(f1);
 assign(f2,'punch.out');rewrite(f2);
 readln(f1,n);
 for i:=1 to n do
 readln(f1,a[i],b[i]);
 fillchar(s,sizeof(s),0);
 fillchar(z,sizeof(z),0);
end;
procedure nb;
var
 i,j:longint;
begin
 m:=0;
 for i:=1 to n do
 begin
 for j:=a[i]+1 to b[i] do
 if z[j]<>i then
             begin
              if z[j]>0 then
               begin
               dec(s[z[j]]);
               if s[z[j]]=0 then dec(m);
               end;
              z[j]:=i;
              if s[i]=0 then inc(m);
              inc(s[i]);
             end;
 end;
end;
begin
 init;
 nb;
 write(f2,m);
 close(f1);close(f2);
end.