#!/bin/python

def solve():
	num = int(input())
	array = list(map(int, input().split()))

	res = 0

	for i, n in enumerate(array):
		if i != n-1:
			for j, m in enumerate(list(array[i+1:])):
				index = j+i+1
				if m == i+1:
					res += 1
					array[index], array[i] = array[i], array[index]
					break
					
	print(res)


def main():
	try:
		while True:
			solve()
	except:
		pass

main()