OEIS A228297: Need Help to Find Algorithm

[Gerald H]

I have run up against a new problem.

If you use

N 5 / IP

to find the integer quotient of N divided by 5 on a 42S an erroneous answer is returned for large numbers, eg for

999999999999

the answer is

200000000000

whereas it should be

199999999999

I have a programme to do the calculation correctly without disturbing the stack but believe it is inefficient.

Could someone suggest a more efficient programme that leaves the stack intact?

Code:

0.    { 29-Byte Prgm }
1.    LBL “IQT5”
2.    R↑
3.    STO 01
4.    R↓
5.    STO 02
6.    5
7.    MOD
8.    +/-
9.    RCL+ 02
10.    5
11.    /
12.    R↑
13.    X<> 01
14.    R↓
15.    END