```
matrix = {
1000:{
1: 'M',
2: 'MM',
3: 'MMM'
},
100:{
1: 'C',
2: 'CC',
3: 'CCC',
4: 'CD',
5: 'D',
6: 'DC',
7: 'DCC',
8: 'DCCC',
9: 'CM'
},
10:{
1: 'X',
2: 'XX',
3: 'XXX',
4: 'XL',
5: 'L',
6: 'LX',
7: 'LXX',
8: 'LXXX',
9: 'XC'
},
1:{
1: 'I',
2: 'II',
3: 'III',
4: 'IV',
5: 'V',
6: 'VI',
7: 'VII',
8: 'VIII',
9: 'IX'
}
} # matrix ends
rm = ''
for i in [1000, 100, 10, 1]:
a = num / i
b = num % i
if a != 0:
rm += matrix[i][a]
num = b
return rm
```