Answer and Explanation:
#take input from user
n = int(input("Enter any number: "))
#sum variable to store sum
sum=0
#condition to exit from loop
while n!=-999:
#adding entered number in sum variable
sum=sum+n
#take input from user
n = int(input("Enter any number : "))
#print the sum
print("sum =",sum)
output:
Enter any number: 10
Enter any number : 100
Enter any number : -999
sum = 110