题解 | #DNA序列#

while True:
    try:
        s, n = input(), int(input())
        if n >= len(s):
            print(s)
        else:
            Max, beg, end = 0, 0, 0
            for i in range(len(s)-n):
                count = s[i:i+n].count('C') + s[i:i+n].count('G')
                if count > Max:
                    Max = count
                    beg, end = i, i+n
            print(s[beg:end])
    except:
        break