Find the smallest possible value of the expression ⌊da+b+c⌋+⌊ab+c+d⌋+⌊bc+d+a⌋+⌊cd+a+b⌋
in which a, b, c, and d vary over the set of positive integers.(Here ⌊x⌋ denotes the biggest integer which is smaller than or equal to x.) functionfloor functionalgebra unsolvedalgebra