c# - System.Configuration.ConfigurationManager.AppSettings not working -

below app.config file

<configuration>   <appsettings>     <add key="input_file" value="d:\bioen\web\newuser\dotnet\passwordgenerator\autopassword\autopassword\passwords.txt"/>     <add key="location" value="sequals"/>   </appsettings> </configuration> 

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when attempt read values in program shown below, both strings null. why this?

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string path = system.configuration.configurationmanager.appsettings["input_file"]; string location = system.configuration.configurationmanager.appsettings["location"];