题解 | #DNA序列#

while True: try: s = input() zclen = int(input()) slen = len(s) GCR = 0 result = [0,'']

    for i in range(slen):
        teststr = s[i:zclen+i]
        GCR = teststr.count('G')+teststr.count('C')
        if len(teststr) == zclen and result[0] < GCR:
            result[0] = GCR
            result[1] = teststr
    print(result[1])

except:
    break