dic={0:''};order=0;s=''
for i in range(int(input())):
  t=[_ for _ in input().strip().split()]
  if t[0]=='1':order+=1;s+=t[1];dic[order]=s
    
  elif t[0]=='3':print(s[int(t[1])-1])
  
  elif t[0]=='2':s=s[:len(s)-int(t[1])];order+=1;dic[order]=s
  
  elif t[0]=='4':order-=1;s=dic[order]