Problem Statement

You are given a permutation $p_1,p_2,...,p_N$ consisting of $1$,$2$,..,$N$. You can perform the following operation any number of times (possibly zero):

Operation: Swap two adjacent elements in the permutation.

You want to have $p_i ≠ i$ for all $1≤i≤N$. Find the minimum required number of operations to achieve this.

Constraints

• $2≤N≤10^5$
• $p_1,p_2,..,p_N$ is a permutation of $1,2,..,N$.

Input

The input is given from Standard Input in the following format:

N
p_1 p_2 .. p_N

Output

Print the minimum required number of operations