Conversion of string to int using digits at beginning

Table contains CHAR(20) type columns containing numbers and other values.

I need to obtain max integer considering only numbers from start of column
up to first non-integer character.

I tried

create temp table test (test char(20));
insert into test values ('12');
insert into test values ('23/3');
insert into test values ('AX/3');
select max(test::int) from test;

but got

ERROR:  invalid input syntax for integer: "23/3      "

How to fix this so that this query returns 23 without error ?

Andrus.