Primary Key

Hi

I try to do the following in a table that has 4 columns,

id - month - day- time

The column id is the primary key, for example

id - month . day - time
1    Jan          22   16:15
2    Jan       22   16:16
3    Jan       22   16:17
4    Jan       22   16:18

But I pretend that automatically when I made an INSERT INTO table (month,
day, time) values (A,B,C) the primary key update his value increasing by one


I dont know how to do this, Iam using Postgres 7.4 with PgAdminIII

Thank you