Cell handlling in excel

I am working in excel. Suppose I have two columns.In first column, there are some zero and some non zero values. The second column is blank. If there is a non zero value in a cell of first column, the same value should be written in the next column. But if the value is a zero, then the previous non zero value in the first column should be written in the second column. So, in the end, The second column gets filled with all non zero values. Please help me out on this one. Thanks, Abhi