Get SPWeb or SPSite URL in sharepoint 2013 workflow in visual studio 2012

I am calling a webservice from my workflow but right now I am specifying the url for webservice with http-://sp2013/_vti_bin/myservice.svc  but I need that this will be something like CurrentWebUrl + "_vti_bin/myservice.svc" and right now I am unable to find this value....Or how to get URL for spsite os spweb in workflow in visual studio 2012...Hmm...Thank you

PS:If I simple use "/_vti_bin/myservice.svc" this is not working. Hmm...Thanks

 I right now found this. There is a WebUri property in toolbox in SP Current Context section. Thanks