You don't need Monte Carlo, you just need a table with three rows. GGC, GCG, CGG. Pick the first door, cross out the other goat, and switch. you will lose once

You don't need Monte Carlo, you just need a table with three rows. GGC, GCG, CGG. Pick the first door, cross out the other goat, and switch. you will lose once and win twice. if for some reason you think the door you pick at first matter somehow, make nine rows, and you will lose three times in win 6. Easy peasy.