Substing Cost Optimimisation

substring_cost.py

cost = 0
initial_string = ""
initial_list = []

def get_all_substrings(input_string):
  length = len(input_string)
  return [input_string[i:j+1] for i in range(length) for j in range(i,length)]

#This takes the input indefenitely
while True:
    input_string = input("Please Enter the String")
    if input_string in set(get_all_substrings(initial_string)):
        cost+=15
    else:
        cost+=10
    initial_string = initial_string + input_string

    print(" Input string : {} \n Current String:{} \n Cost:{}".format(input_string,initial_string,cost))