def longest_consec(strarr,k):
n = len(strarr)
chr_len = {}
if n ==0 or k > n or k <= 0:
return ''
else:
for idx in range(1,len(strarr)+1):
length = len(strarr)
chr_len[strarr[idx]] = length
for k in chr_len.keys():
if chr_len[k]
#用字典排序
return ''.join(strarr[-2:])
if __name__ == '__main__':
strarr = list(input('请输入字符串元素(用逗号分隔): ').split(','))
k = int(input('请输入需要取出的字符串个数: '))
print(longest_consec(strarr, k))