Filling in empty cells

[cokeblue8]

Hi I'm new at programming Excel, so I apologize in advance if this is really elementary.

I want to fill in all the empty cells with the value '0' only if the empty cells are between two non-empty cells less than 4 cells away. Otherwise, the cells should be left blank.

I.e. for:
5 | 6 | | | 6 | | 5 | 6 | | (think of | as separating two cells)

all the blanks should be replaced by 0.

For

5 | | | | | | | 6 |

none of them should be replaced by 0. (because the cells are between two non-empty cells more than 4 cells away.)

Thanks everyone in advance!!