def func(s):
	for l in range(1, len(s) + 1):
		r = s[:l]
		if len(r) * 2 > len(s):
			return s
		f = True
		for m in range(l * 2, len(s) + 1, l):
			if r != s[m - l:m]:
				f = False
				break
		if f:
			break
	return r

print(func('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'))
print(func('123412312341231234123123412312341231234123'))
print(func('oxoxoxoxoxoxoxoxxoxoxoxoxoxoxoxoxx'))
print(func('abac'))