Why am i getting no error but the code isnt working?

I am trying to write a code for class that identifies the probability that two or more people given can have the same birthday out of a group by running this experiment 10^6 times and then calculating the fraction of times during which two or more people had the same birthday. I attached the code below, but when I try and run it absolutely nothing happens. It gives no error message, it just stops working. Does anyone have an idea why?

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 import random

 def calc_birthday_probability (num_people):

 random.seed (2020) # Don't change this value
 num_trials = 1000000
 probability = 0
 list1 = []
 num_people = int(input())
 repeats = 0
 for i in range(0,num_trials+1):

     for i in range (0,num_people+1):
        list1.append(random.randint (1,3655))
        for i in list1:
            if list1.count(i)>1:
                repeats +=1
                i = i+1
            i = i+1

prob = repeats//num_trials
probability = probability + prob

return probability

a = calc_birthday_probability(10)

print(a)