A = [10, 20,.... 500]
 B = [1, 4,.... 2500]

def func():
    x = input("enter a value from the array A: ") #user input
    for i in range(50):
       if A[i] == x:
          print(B[i])

       else:
          print("do nothing")

func()

A = [10, 20,.... 500]
  B = [1, 4,.... 2500]

  def func():
     x = int(input("enter a value from the array A: ")) #user input
     for i in range(50):
       if A[i] == x:
         print(B[i])

       else:
        print("do nothing")

  func()

A = [10, 20,.... 500]
B = [1, 4,.... 2500]

def func():
    x = int(input("enter a value from the array A: ")) #user input
    for i,v in enumerate(A):
        if v == x:
            print(B[i])
            break

    else:
        print("do nothing")

func()

def func():
   x=int(input("enter a value from the array A: "))
   if x in A:
       idx = A.index(x)
       print(B[idx])
   else:
       print("do nothing")