Oracle Database Discussions

Following is the layout of my table, Status Column can have 1,2,3....6 . My requirement is that CNIC column can not be duplicate if status = 1, this can be duplicate for other status types.
This table has about 0.5 Million Records.

CREATE TABLE TARIQ_CORE.pensioner
(
  claim_no        VARCHAR2(25),
  cnic            VARCHAR2(13),
  status          NUMBER(1),
  name            VARCHAR2(35),
  pension_amount  NUMBER(5)
);

ALTER TABLE TARIQ_CORE.pensioner ADD (
  CONSTRAINT pensioner_PK
  PRIMARY KEY
  (claim_no));

How can i manage this.