题解 | #DNA序列#

DNA = input()
N = int(input())
ratio = {}
r = []
for i in range(len(DNA) - N + 1):
    a = DNA[i : i + N]
    g = a.count("G")
    c = a.count("C")
    gc = g + c
    ratio[a] = gc

m = max(ratio.values())
for k, v in ratio.items():
    if v == m:
        r.append(k)
# k2 = [k for k, v in ratio.items() if v == m]
# print(k2)
print(r[0])