The Romans had their own counting system that was different from ours - you might have seen it used for dates on some buildings and at the end of television programmes or films.
They used the letters I, V, X, L, C, D and M to represent the values 1, 5, 10, 50, 100, 500 and 1000 respectively. There shouldn't really be more than three of the same letter in a row. Letters with a bar over the top are multiplied by 1000, e.g. X is 10,000.
Type a number into the dotted box to see what it would look like when written in Roman numerals.