Get Guid from the PartyList in CRM 2011 using C#

Entity entity = (Entity)context.InputParameters["Target"];
var retrievedApprovalRequest = service.Retrieve(entity.LogicalName, entity.Id, new ColumnSet(true)).ToEntity<tvsi_approvalrequest>();

Guid salesmanagerId=new Guid();              
ActivityParty ap=new ActivityParty();
EntityCollection receiverIds = retrievedApprovalRequest.GetAttributeValue<EntityCollection>("to");
 for (int i = 0; i < Recipients.Entities.Count; i++)
 {
      ap = receiverIds[i].ToEntity<ActivityParty>();
      salesmanagerId = ap.PartyId.Id;                  
 }