题解 | #DNA序列#

while True:
    try:
        dna = input()
        n = int(input())
        lst = []
        for i in range(len(dna)):
            lst.append(dna[i: i + n])
        ratio = 0
        ans = ''
        for item in lst:
            nc = item.count('C')
            ng = item.count('G')
            if (nc + ng) / n > ratio:
                ratio = (nc + ng) / n
                ans = item
        print(ans)
    except:
        break