#include <bits/stdc++.h>
using namespace std;

int main()
{
	int N;
	cin >> N;
	vector<int> P( N );
	for( int i = 0; i < N; i++ ) cin >> P[i];

	long long ans = 0;
	for( int i = 0; i < N; i++ ) {
		if( P[i] == i + 1 ) continue;
		for( int j = i + 1; j < N; j++ ) {
			if( P[j] == P[i] - 1 ) {
				swap( P[j], P[i] );
				ans++;
				break;
			}
		}
		if( P[i] > i + 1 ) i--;
	}

	cout << ans << endl;
}