Period

def find_shortest_period(string):
    if len(set(string)) == 1:
        return string[0]
    n = len(string)
    for i in range(1, len(string) + 1):
        # print(f"checking period size {i}")
        substring = string[:i]
        is_period = True
        for j in range(i, len(string), i):
            for k in range(i):
                if j+k >= n:
                    break
                # print(j, k)
                if substring[k] != string[j+k]:
                    is_period = False
                    break
            if not is_period:
                break
        if is_period:
            return substring


string = input()
print(find_shortest_period(string))

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: TIME LIMIT EXCEEDED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED