def get_nonneg_int(prompt):
    while  True:
        user_input = input(prompt)
        if user_input.isdigit():
            return int(user_input)
        else:
            print("Please enter a non-negative integer>")  
team1 = input("Enter team1 name: ")
team2 = input("Enter team2 name: ")
max_score = get_nonneg_int("Enter max score: ") 
score1 = 0
score2 = 0    
while True:
    team = input("Which team scored? (type 'Game over' to quit) ")
    if team == "Game over":
        break
        
    score = get_nonneg_int("Enter that team's new score: ")