A credit portfolio from year-2000 vintage now contains 20 low risk and 7 high risk loans. Every month a loan gets selected at random and gets discarded from the portfolio. If the loan is low risk a prepayment occurs and a reward of 1 is obtained. If it is high risk a default occurs and a loss of -2 is sustained. One is allowed to stop the process at a time when the expected payoff from not stopping turns negative. With 7 high risk loans remaining how low should the number of low risk loans get to be optimal to stop the process?