var f,g:text;
    n:integer;
    i,j:longint;
    v:array[1..7999,1..2] of longint;
    s:longint
procedure load;
begin
assign(f,'heavymetal.in');
reset(f);
readln(f,n); s:=0;
for i:=1 to n do
for j:=1 to 2 do
read(f,v[i,j]);
for i:=1 to  n do
if v[i,2]-v[1,i+1] > 0 then
s:=s+(v[i,2]-v[1,i]);
close(f);
end;
procedure scris;
begin
assign(f,'heavymetal.out');
rewrite(f);
writeln(s);
close(f);
end;
BEGIN
load;
scrie;
END.