This algorithm converts Roman numerals to a numeric decimal integer

RomanToInt.cs

using System.Collections.Generic;

public class RomanToInt
{
    public static int Decode(string roman)
    {
      var dict = new Dictionary<char,int>(){
        {'M',1000},
        {'D',500},
        {'C',100},
        {'L',50},
        {'X',10},
        {'V',5},
        {'I',1}
      };
      
      int num = 0;
      
      for(int i=0; i<roman.Length; i++){
        // iv, ix, xl, xc, cd,cm
        switch(roman[i]){
          case 'I':
            if(i < roman.Length-1){
              if(roman[i+1] == 'V') {
                num += 4;
                i++;
                break;
              }
              if(roman[i+1] == 'X') {
                num += 9;
                i++;
                break;
              }
            }
            num += dict[roman[i]];
            break;
           case 'X':
            if(i < roman.Length-1){
              if(roman[i+1] == 'L') {
                num += 40;
                i++;
                break;
              }
              if(roman[i+1] == 'C') {
                num += 90;
                i++;
                break;
              }
            }
            num += dict[roman[i]];
            break;
           case 'C':
            if(i < roman.Length-1){
              if(roman[i+1] == 'D') {
                num += 400;
                i++;
                break;
              }
              if(roman[i+1] == 'M') {
                num += 900;
                i++;
                break;
              }
            }
            num += dict[roman[i]];
            break;
          default:
            num += dict[roman[i]];
            break;
        }
      }
      
      return num;
    }
}