#Nicholas Jones p149676.
#(3) Add up numbers program
total = 0
ui = 0

print("Hello.")

while ui != -1:    
    ui = int(input("Enter number (-1 to exit): "))
    if ui >=0:
        total = total + ui
    else:
        if ui <0:
            print("you cannot input a negative number.")
print("Your total is {} ".format(total))