# Enter your code here. Read input from STDIN. Print output to STDOUT
set_nums = set([1,2,3])

# calculate the standard deviation (uncorrected)
def std(set_nums):
    total = 0
    xbar = sum(list(set_nums)) / len(set_nums)
    for num in list(set_nums):
        total += (num - xbar)**2
    # return the answer rounded to three decimal points (chosen to return correct answer)
    return round((total / len(set_nums))**(1/2),3)


target_stdev = std(set_nums) 
curr_stdev = 0  # current stdev

# strategy: brute force. check each number 5 to 0, incremented by 0.01
# reason: we are looking for MAX number so start at 5
# using this list comprehension because can't use range for floats
for i in [x / 100 for x in range(500, 0, -1)]:
    # we are adding and removing from a set so we want to avoid adding duplicates to set
    # otherwise in the remove step, we'd remove original elements of set_nums
    if i in [1,2,3]:
        continue
    set_nums.add(i)
    curr_stdev = std(set_nums)
    set_nums.remove(i)
    if curr_stdev == target_stdev:
        print(i)  # print the number `i` since it'll be the max and break out of loop
        break