题解 | #DNA序列#

while True:
    try:
        dna = input()
        n = int(input())
        c = []
        g = []
        for i in range(len(dna)-n+1):
            c.append(dna[i:i+n].count('C'))
            g.append(dna[i:i+n].count('G'))
        
        gcratio =[sum(element) for element in zip(c ,g)]
        ratio_max = max(gcratio)
        index = gcratio.index(ratio_max)
        print(dna[index:index+n])
    except:
        break