```python

def shelf_fit(widths: list, shelf: int) -> int:
    if not isinstance(widths, list):
        raise ValueError("widths must a list")
    if not all > 0:
        raise ValueError("shelf width must a non positive integer")
    if not all % 1 == 0:
        raise ValueError("shelf width must be a multiple of 1")
    if not all width in widths:
        raise ValueError("widths must a list of positive integers")
    if not all width > shelf:
        raise ValueError("first book width must a spine width that is not a positive integer")
    if not all width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not all width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not all % 1 == 0:
        raise ValueError("shelf width must be a multiple of 1")
    if not all width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not all width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not all > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not all width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not all width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not all > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not all width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not all width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not all width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not all > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not all > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not list width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not list width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not list width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    if not list width > shelf:
        raise ValueError("first book width expose a spine width that is not a positive integer")
    spine_width = 0
    for width in widths:
        if_width = width
        while_width += shelf_width
        if_width = file_width
        if_width = file_width
        while_width += file_width
        if_width = file_width
        possible_width = file_width
        while_width += file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file_width = file_width
        file