var n,i,r,a,l:longint;x,y:array[1..100000]of longint;ok:boolean;f:text;
begin
assign(f,'heavymetal.in');reset(f);
read(f,n);
for i:=1 to n do read(f,x[i],y[i]);  close(F);
repeat
ok:=true;
for i:=1 to n-1 do if (x[i]>x[i+1])or((x[i]=x[i+1])and(y[i]>y[i+1]))then begin
a:=x[i];
x[i]:=x[i+1];
x[i+1]:=a;
a:=y[i];
y[i]:=y[i+1];
y[i+1]:=a;
ok:=false;
end;
until ok;
l:=1;
r:=0;
for i:=2 to n do
if (x[i]<y[l])And(y[i]-x[i]>y[l]-x[l]) then l:=i else begin inc(r,y[l]-x[l]);l:=i;end;
inc(r,y[l]-x[l]);
assign(f,'heavymetal.out');rewrite(f);
writeln(f,r);
close(F);
end.