number = input("Enter your total natural numbers")
first_num = input("Enter your first number")
last_num = input("Enter your last number")
print ("Your first first and last number of n natural number is : " + str(first_num) + str(last_num))
natural_number = (first_num + last_num) * number / 2
print ("The n natural number of first number " + str(first_num) + " and last number " + str(last_num) + " is " + str(natural_number))