N persons are standing in a circle labelled from 1 to N in clockwise order. Every one of them is holding a gun and can shoot a person on his left. Starting from person 1, they starts shooting in order e.g for N=50, person 1 shoots person 2, then person 3 shoots person 4, then person 5 shoots person 6……..then person 49 shoots person 50, then person 1 shoots person 3, then person 5 shoots person 7……and it continues till all are dead except one. What is the index of that last person?