Answer:
In Python:
num = int(input("Enter number: "))
maxn = num
while num >=0:
  if num>maxn:
    maxn = num
  num = int(input("Enter number: "))
print("Largest: "+str(maxn))
Explanation:
Get input from the user
num = int(input("Enter number: "))
Initialize the largest to the first input
maxn = num
This loop is repeated until a negative input is recorded
while num >=0:
If the current input is greater than the previous largest
  if num>maxn:
Set largest to the current input
    maxn = num
Get another input from the user
  num = int(input("Enter number: "))
Print the largest
print("Largest: "+str(maxn))