CF892B Wrath

Hands that shed innocent blood! There are $ n $ guilty people in a line, the $ i $ -th of them holds a claw with length $ L_{i} $ . The bell rings and every person kills some of people in front of him. All people kill others at the same time. Namely, the $ i $ -th person kills the $ j $ -th person if and only if $ j=i-L_{i} $ . You are given lengths of the claws. You need to find the total number of alive people after the bell rings.