处理输入花了很长时间

import sys
def get_ans(s,n):
    return s[:n]

if __name__=='__main__':
#输入一个数/字符串
    lines = []
    while True:
        line = sys.stdin.readline().strip()
        if line == "":
            break
        lines.append(line)
    for i in range(int(len(lines)/2)):
        s_in=lines[2*i]
        n_in=int(lines[2*i+1])
        print(get_ans(s_in,n_in))