Another present-day convention is the avoidance of more than three consecutive occurrences of the same letter in favor of the more succinct forms achieved by using the subtraction principle -- for example, IV for IIII (4), XL for XXXX (40), and CD for CCCC (400). An exception is the numeral M, or 1000, which is used 4 times to represent our number 4000, since the Romans had no single-letter numeral representing a higher value than M. It is now also customary not to repeat the values V, L, or D (5, 50, or 500) in the same numeral.