How to redirect previous visualforce page from current visualforce page?

Hi Everyone,

 First of all here i'm having two visualforce pages
 
 1.Webinar_Details Page
 2.MappingLeadPage
 
 webinar_details page is a record details page it displays all the details of one particular record.
 In this page i'm having a button calles "Mapping Lead" by clicking the button it redirects to the
 "MappingLeadPage" visualforce page.after mapping the fields i'm saving the mapping and redirects to the previous record
 details page.
 
 here for redirecting i need the previous record id.how can i get the previous record id for redirecting
 
 Webinar_Details Page
 --------------------
 <apex:page standardController="Webinar__c" tabstyle="Adobe_Webinars__tab" sidebar="false" extensions="RedirectPage">
    
    <apex:form >   
     <apex:pageBlock title="Adobe Connect Integration with Salesforce">
         <center>         
           <apex:commandButton value="Register" action="{!doRegistrationForm}"/>     
         </center><br/><br/>
         <apex:pageBlockSection title="{!Webinar__c.Name} Details">
            <apex:outputField value="{!Webinar__c.Name}"/>      
            <apex:inlineEditSupport event="ondblClick" /><br/>                    
         </apex:pageBlockSection><br/>         
    </apex:pageBlock>           
          <apex:pageBlock >
            <apex:pageBlockTable value="{!wrapperAccountList}" var="w" id="table" title="All Accounts">
                 <apex:column value="{!w.acc.Login__c}"></apex:column>
                 <apex:inlineEditSupport event="ondblClick" />
                 <apex:column value="{!w.acc.isLead__c}"></apex:column>                                
            </apex:pageBlockTable>
        </apex:pageBlock>
               
         <center>
              <apex:commandButton id="leadcreate1" value="Lead Mapping" action="{!doMappingPage}"/>
          </center><br/>   
    </apex:pageBlock>      
 </apex:form>         
</apex:page>

extension:
-----------

 public class RedirectPage{
 
        public PageReference doMappingPage(){            
        PageReference parentPage = new PageReference('/apex/MappingLeadPage');
        parentPage.setRedirect(true);
        return parentPage;
  }
 
}

MappingLeadPage
----------------
<apex:page standardController="Lead" extensions="MappingLead1">    
  <apex:form >  
    <apex:pageBlock title="Lead Mapping" >             
      <apex:pageBlockSection >       
        <apex:pageBlock >            
           <apex:pageBlockSection >          
                   Webinar Attendee Name  <apex:inputField value="{!Lead.LeadFields__c}"/><br/>  
                   Webinar Attendee Email <apex:inputField value="{!Lead.Lead_Fields1__c}"/><br/>
                   Webinar Attendee Company  <apex:inputField value="{!Lead.Lead_Fields2__c}"/><br/>  
               Webinar Attende Mobile Number <apex:inputField value="{!Lead.Lead_Fields7__c}"/><br/><br/>
                  <!--   <apex:outputLink value="{!URLFOR($Page.Webinar_Details,w.acc.Id,[id=w.acc.Id])}">{!w.acc.name}</apex:outputLink>    -->         
            
         </apex:pageBlockSection>
            <apex:commandButton id="saveBtn" value="Save Mapping" action="{!processButtonClick}" style="margin-left:-2%"/>                                          
               <apex:commandButton id="saveBtn1" value="Previous Page" action="{!goBack}" style="margin-left:30%"/>                                          
            <apex:pageBlockButtons >
            </apex:pageBlockButtons>
       </apex:pageBlock>   
     </apex:pageBlockSection>     
   </apex:pageBlock>                
  </apex:form>
</apex:page>


extension
------------
public with sharing class MappingLead1  {
    public Lead login;
    private final ApexPages.StandardController controller;                  
    public MappingLead1(ApexPages.StandardController controller){       
        this.login= (Lead)controller.getRecord();  
    }

    public PageReference goBack(){
    PageReference pg = new PageReference('/apex/Webinar_Details');
    pg.setRedirect(true);
    return pg;
  }
}

from the MappingLeadPage page by clicking the "Previous Page" button how i redirected to the Webinar_Details Page vf page.

Please anybody help i'm trying this logic from yesterday

Thanks In Advance