program ooo;
var
t:text;
a:array[1..50000,1..2] of longint;
b:array[1..50000,1..2] of boolean;
c:array[1..50000] of integer;
o,x,y,j,k,i:longint;
begin
assign(t,'pie.in');
reset(t);
readln(t,o);
for i:=1 to o do
readln(t,a[i,1],a[i,2]);
close(t);
i:=1;
j:=0;
while i<o do
begin
 if (a[i,2]=a[i+1,1]) then begin
if (b[i,1]<>true)and(a[i,1]<>a[i-1,2]) then begin
inc(j);
b[i,1]:=true;
c[j]:=a[i,1];
end;
if (b[i,2]<>true) then begin
inc(j);
b[i,2]:=true;c[j]:=a[i,2]
end;
if (b[i+1,2]<>true) then begin
inc(j);
b[i+1,2]:=true;c[j]:=a[i+1,2];
end;


end;
inc(i);
end;

assign(t,'pie.out');
rewrite(t);
write(t,j);
close(t);
end.