python: rename images

rename.py

import os
import shutil
import time

dir = raw_input()+"/"


if os.path.isdir(dir):  
    print ("Directory is exit")
else:
    print ("Directory is not exit,please input right dir....") 
    time.sleep(5)    
    exit()            
filelist=[]

filelist=os.listdir(dir) 
#print filelist

count=0
for i in filelist:
    if '.jpg' in i:
        NewFile=str(count)
        count=count+1
        print NewFile     
       
        shutil.move(dir+i,dir+NewFile+'b.jpg')