LP28 plan is based on the series of 28 multipliers which are applied consequently to your Stake. The series is:
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 5, 5, 6, 6, 7
Every time you lose, the plan goes one step forward in the series. If you win, the sequense starts again from first number.
So the lowest possible bet would be your Stake x 1 and the highest Stake x 7.