题解 | #DNA序列#

s = input()
N = int(input())
ls = []
for i in range(0, len(s)):
    ls.append(s[i : i + N])
#print(ls)
lst = []
for i in ls:
    if len(i) == N:
        lst.append(i)
#print(lst)
lsd = []
p = 0
for i in lst:
    if ((i.count("G")) + (i.count("C"))) / len(i) > p:
        lsd.append(((i.count("G")) + (i.count("C"))) / len(i))

print(lst[lsd.index(max(lsd))])  # 注意这个的写法