照着跑，能走到第几步

四步说明，仓库里缺一个文件。运行下面这段程序，看成功跑过几步、卡在第几步：

def dry_run(steps, files):
    for i, (cmd, need) in enumerate(steps, 1):
        if need and need not in files:
            return i, need
    return 0, None

steps = [('git clone https://example.com/calc.git', None),
         ('cd calc', None),
         ('pip install -r requirements.txt', 'requirements.txt'),
         ('python main.py', 'main.py')]
files = ['main.py', 'calc.py', 'README.md']
i, _ = dry_run(steps, files)
print(str(i - 1) + "/" + str(i))