var res,n,i,a,b,a1,b1:longint;
begin
    readln(n);readln(a1,b1);readln(a,b);
    If (a = a1) then res :=1
    else if (b = b1) then res :=2
    else
    begin
        writeln('NO');exit;
    end;
    a1 :=a;b1 :=b;
    For i:=3 to n do
    begin
        readln(a,b);
        If ((a = a1) and (res = 2)) or ((b = b1) and (res = 1)) or ((a <> a1) and (b <> b1)) then
        begin
            writeln('NO');exit;
        end;
        a1 :=a;b1 :=b;
    end;
    writeln('YES');
end.