program STARWAR;

{$APPTYPE CONSOLE}

const inpf='Corusant.DAT';
      outf='Corusant.SOL';

type
  list = array[1..20000] of integer;

var f:text;

    i,n,n2,kilkx,kilky,zx,zy,zx1,zy1,m,b1,b2:integer;
    x,y,x1,y1,cx,cy:list;
    aa:array [1..20000,1..20000] of byte;
    area:Cardinal;

procedure quicksort(var a: list; Lo,Hi: integer);

procedure sort(l,r: integer);
var
  i,j,x,y: integer;
begin
  i:=l; j:=r; x:=a[(l+r) DIV 2];
  repeat
    while a[i]<x do i:=i+1;
    while x<a[j] do j:=j-1;
    if i<=j then
    begin
      y:=a[i]; a[i]:=a[j]; a[j]:=y;
      i:=i+1; j:=j-1;
    end;
  until i>j;
  if l<j then sort(l,j);
  if i<r then sort(i,r);
end;

begin {quicksort};
  sort(Lo,Hi);
end;

procedure bulbaska(var a:list; lo,hi:integer);
var ii,jj,r:integer;
begin
for ii:=lo to hi-1 do
  for jj:=ii+1 to hi do
    if a[ii]>a[jj] then
      begin
      r:=a[ii];
      a[ii]:=a[jj];
      a[jj]:=r;
      end;
end;

function binfind(d:list; lo,hi,s:integer):integer;
var v,l,h:integer;
begin
l:=lo;
h:=hi;

while true do
  begin
  if l+h mod 2=0 then v:=(l+h-1) div 2 else v:=(l+h) div 2;
  if (s<d[v]) then h:=v-1 else
  if (s>d[v]) then l:=v+1 else
    begin
    Result:=v;
    exit;
    end;
  if l>h then
    begin
    Result:=-1;
    Exit;
    end;
  end;
end;

begin

Assign (f,inpf);
reset (f);
readln (f,n);
n2:=2*n;
for i:=1 to n2 do
if odd(i) then
    begin
    read(f,x[i],y[i]);
    cx[i]:=x[i];
    cy[i]:=y[i];
    end
  else
    begin
    readln (f,x[i],y[i]);
    cx[i]:=x[i];
    cy[i]:=y[i];
    end;

close (f);

if n2>100 then
  begin
  quicksort (cx,1,n2);
  quicksort (cy,1,n2);
  end
else
  begin
  bulbaska(cx,1,n2);
  bulbaska(cy,1,n2);
  end;

kilkx:=0;
kilky:=0;

for i:=1 to n2 do
  begin

    if i<>1 then
      begin
      if cx[i]<>cx[i-1] then
        begin
        inc(kilkx);
        x1[kilkx]:=cx[i];
        end;
      if cy[i]<>cy[i-1] then
        begin
        inc(kilky);
        y1[kilky]:=cy[i];
        end;
      end
    else
      begin
      kilkx:=1;
      kilky:=1;
      x1[1]:=cx[1];
      y1[1]:=cy[1];      
      end;

  end;

i:=1;
while i<=n2 do
  begin

  zx:=binfind(x1,1,kilkx,x[i]);
  m:=zx+1;
  while x1[m]<>x[i+1] do
  inc(m);
  zx1:=m;

  zy:=binfind(y1,1,kilky,y[i]);
  m:=zy+1;
  while y1[m]<>y[i+1] do
  inc(m);
  zy1:=m;

  for b1:=zx to zx1-1 do
  for b2:=zy to zy1-1 do
  if aa[b1,b2]=0 then
    begin
    aa[b1,b2]:=1;
    inc(area,(x1[b1+1]-x1[b1])*(y1[b2+1]-y1[b2]))
    end;

  inc(i,2);
  end;

assign (f,outf);
rewrite (f);
writeln (f,area);
close (f);

end.