题解 | #DNA序列#

while True:
try:
s=str(input())
n=int(input())
i=0
c_max=''
GCcount=0
index=0
while i+n<=len(s):
if s[i:i+n].count('G')+s[i:i+n].count('C')> GCcount:
index=i
c_max=s[index:index+n]
GCcount=c_max.count('G')+c_max.count('C')
i+=1
print(c_max)
except:
break