please check the format

[vinit005]

if (!(GetField(header, fields, "Declared Value for Carriage").Equals("") || GetField(header, fields, "Declared Value for Carriage").Equals(null)) && !(GetField(header, fields, "Number of Packages").Equals("") || GetField(header, fields, "Number of Packages").Equals(null)))
                        {
                            writer.WriteElementString("InsuranceAmount", (int.Parse(GetField(header, fields, "Declared Value for Carriage")) / int.Parse(GetField(header, fields, "Number of Packages"))).ToString());
                            //writer.WriteElementString("InsuranceAmount", "");
                        }
                        else
                        {
                            writer.WriteElementString("InsuranceAmount", "");
                            //writer.WriteElementString("InsuranceAmount", (Convert.ToInt16(GetField(header, fields, "Declared Value for Carriage")) / Convert.ToInt16(GetField(header, fields, "Number of Packages"))).ToString());
                        }

i m getting error in the third line .the error states that the input string format is not correct.please help me............