Backup in oracle db using triggers

I have 2 identical tables, just change the name table1 and table2 , when you enter 3 records in table1 the information in this table must be copied to table 2 and table 1 must be empty again.

  

The solution must be reached using triggers.

I have the following code

CREATE TABLE TABLA1(
ID_1 NUMBER PRIMARY KEY, NOMBRE VARCHAR2(40));

CREATE TABLE TABLA2(
ID_1 NUMBER PRIMARY KEY, NOMBRE VARCHAR2(40));

SELECT * FROM TABLA1;
SELECT * FROM TABLA2;


SET SERVEROUTPUT ON;
CREATE OR REPLACE TRIGGER DISP_BACKUP
BEFORE INSERT ON TABLA1
FOR EACH ROW
DECLARE
CURSOR CUR_CUENTA IS SELECT * FROM TABLA1;
--CURSOR CUR_CUENTA IS SELECT COUNT(*) FROM TABLA1;
var_rows := SQL%ROWCOUNT;
--CURCHOISE SQL%ROWCOUNT;
BEGIN
dbms_output.put_line('NUMERO DE REGISTROS EN TABLA 1' || CUR_CUENTA%ROWCOUNT 
);
--OPEN CUR_CUENTA;
IF CUR_CUENTA%ROWCOUNT > 3 THEN
IF INSERTING THEN
INSERT INTO TABLA2 (ID_1,NOMBRE) VALUES (:NEW.ID_1,:NEW.NOMBRE);
END IF;
DELETE FROM TABLA1;
END IF;
END;
/