private int getValue(char letter) {
        switch (letter) {
            case 'I':
                return I;
            case 'V':
                return V;
            case 'X':
                return X;
            case 'L':
                return L;
            case 'C':
                return C;
            case 'D':
                return D;
            case 'M':
                return M;
            case 'E':
                return E;
        }
        return -1;
    }