file_in = "file_in.txt"
file_out = "file_out.txt"
data = ""

# read the first 3 lines of file_in.txt
with open(file_in, 'r') as f:
    for i in range(3):
        data += f.readline()

# write to file_out.txt
with open(file_out, 'w') as f:
    f.write(data)

# read the content of file_out.txt
with open(file_out, 'r') as f:
    content = f.read()
    print(content)