Now, we know that we can only put three I’s in a row before we have to change them, so the number will end with three I’s. Next, we know that we can’t have two V’s together (that makes an X), so we’ll put one V. The next one up is the X. So, the lowest is: XXVIII (28)

Now, the highest. Since we can’t go above 2000, that gives us one M to start. Now, to get the highest in the hundreds, we want to go with CM (900). Going to the tens, XC (90). This leaves us one character, and the highest we have remaining is V (5)…so, MCMXCV (1995) would be the highest with exactly 6 characters.