Scope of Variable in PL/SQL

SQL> SET SERVEROUTPUT ON;
SQL>
SQL> DECLARE
  2     k   NUMBER := 10;
  3     v   NUMBER := 1;
  4  BEGIN
  5     v := v + 21;
  6  /* Inner block */
  7     DECLARE
  8        s   NUMBER := 0;
  9     BEGIN
 10        s := v;
 11        DBMS_OUTPUT.put_line ('s=' || s); -- can't use outside of this Inner block
 12     END;
 13  /* End Inner block */
 14     DBMS_OUTPUT.put_line ('s=' || s);
 15  END;
 16  /
   DBMS_OUTPUT.put_line ('s=' || s);
                                 *
ERROR at line 14:
ORA-06550: line 14, column 34:
PLS-00201: identifier 'S' must be declared
ORA-06550: line 14, column 4:
PL/SQL: Statement ignored

SQL> SET SERVEROUTPUT ON;
SQL>
SQL> DECLARE
  2     k   NUMBER := 10;
  3     v   NUMBER := 1;
  4  BEGIN
  5     v := v + 21;
  6  /* Inner block */
  7     DECLARE
  8        s   NUMBER := 0;
  9     BEGIN
 10        s := v;
 11        DBMS_OUTPUT.put_line ('s=' || s); -- can't use outside of this Inner block
 12     END;
 13  /* End Inner block */
 14     DBMS_OUTPUT.put_line ('v=' || v);
 15  END;
 16  /
s=22
v=22

PL/SQL procedure successfully completed.