Salesman needs to manage stocks in a n periods. Each period i, salesman know that unit cost of the products p_i, unit cost c_i of selling a product. Unit cost h_i of stocking a products during period i. At each period i salesman cannot stock more than B products. The initial and the final stocks are must be zero. End of period i, salesman sales a given number of y_i product. The salesman wants to maximize the profit. Model this problem as a flow problem in an appropriately constructed graph.