var

n,i,j,k,min,max:longint;

a,b,c:array[-200000000..20000000]of longint;

begin

read(n);

for i:=1 to n do

begin

read(a[i],b[i]);

if a[i]max then max:=b[i] else max:=max;

end;

for i:=1 to n do

if a[i]b[i] then

for j:=a[i] to b[i]-1 do

c[j]:=1;

k:=0;

for i:=min to max do

if c[i]=1

then inc(k)

else k:=k;

write(k);

end.