Need to Capture the initial value of a cell.

HI,

I need to capture the initial value of a cell into another cell, and when the parent cell changes the value, the child cell must still show the initial value.
For Ex : When the excel sheet was opened, say the value of A1 was 25, So I want this value in B1. And now when I change A1 value any number of times, still the B1 value must be 25 itself.

But I have formulas in other cells of the excel sheet, which won't work if I do that.