Man is smoking a cigarette. He can smoke 3/4th of cigarrete and dump 1/4th. You are given the Number of Cigarretes Man have. You need to find the total number of Cigarretes he can smoke. Smoking 3/4 of cigarrete is counted as 1.
For e.g. S=4, Man smokes 3/4 of each cigarrete, so 4 Cigarettes, and dumps 1/4+1/4+1/4+1/4 = 1. That mean Man can smoke one more cigarette from dump. So total number of Cigarretes he can smoke is 4+1 = 5.

For e.g. S=16, 3/4 of each cigarrete, total 16 cigarretes, and 16*1/4 = 4, again 4*1/4 = 1. So total number of Cigarettes he can smoke = 16+4+1 = 21