def common_string(*argv) -> str:
    """Return common begining of input strings."""
    ls_out = []
    for args in zip(*argv):
        arg_1 = args[0]
        flag = all([arg == arg_1 for arg in args])
        if flag:
            ls_out.append(arg_1)
        else:
            break
    return "".join(ls_out)