题解 | #DNA序列#

while True:
    try:
        s, n = input(), int(input())
    except:
        break
    dict01 = {}  # 键:字符串 值: CG频次
    for i in range(len(s) - n + 1):
        dict01[s[i:i+n]] = 0
        for j in s[i:i+n]:
            if j == 'C' or j == 'G':
                dict01[s[i:i + n]] +=1
    r = max(dict01, key=lambda x:dict01[x])
    print(r)