var f,g:text;
    n:integer;
    i,j:longint;
    sir:array[1..2] of longint;
    v:array[1..7999,1..2] of longint;
    s:longint;
procedure load;
begin
assign(f,'heavymetal.in');
reset(f);
readln(f,n);
for i:=1 to n do
for j:=1 to 2 do
read(f,v[i,j]);
s:=v[1,2]-v[1,1];



FOR I:=1 TO N DO
FOR J:=1 TO 2 DO
BEGIN
if (i+j) > 2 then 
if v[i,j]-v[i+1,j-1] > 0 then
s:=s+(v[i,j]-v[i,j-1]);
end;
close(f);
END;

procedure scrie;
begin
assign(f,'heavymetal.out');
rewrite(f);
writeln(f,s);
close(f);
end;
BEGIN
load;
scrie;
END.