while execute the stored procedure it shows the following error?

Question

create or replace procedure insert_state1(p_country_id in state.countryid%type, p_state_name in state.statename%type) is

 v_countryname varchar2(20);

 begin

 select countryname into v_countryname from country where countryid=p_country_id;

 insert into state(countryid, countryname, statename) values(p_country_id,v_countryname,p_state_name);

 end;
/

Procedure created.

SQL> exec insert_state1(10,'ap');

BEGIN insert_state1(10,'ap'); END;

*

ERROR at line 1:

ORA-01422: exact fetch returns more than requested number of rows

ORA-06512: at "SCOTT.INSERT_STATE1", line 4

ORA-06512: at line 1

where is error and how to execute?