ksf-2015-cd-13

Every asterisk in the equation \(2 * 0 * 1 * 5 * 2 * 0 * 1 * 5 * 2 * 0 * 1 * 5 = 0\) is to be replaced with either + or so that the equation is correct.

Question:

What is the smallest number of asterisks that must be replaced with +?