#include <iostream>
#include <stdio.h>

using namespace std;

int solveVeryBigProblem(int *& array, int size) {

	int counter = 0, min = 1;
	
	for(int i = 0; i < size; i++) {
		if(min==array[i] && i != min-1) {
			int tmp = array[i];
			array[i] = array[min-1];
			array[min-1] = tmp;
			counter++;
			i=min;
			min++;
		}
	}

	return counter;

}


int main(void) {

    int n;
    
    while(scanf("%d", &n) != EOF) {
        
        int * array = NULL, tmp;
        array = new int[n];
        
        for(int i = 0; i < n; i++) {
            scanf("%d", &tmp);
            array[i] = tmp;
        }
        
        cout << solveVeryBigProblem(array, n) << endl;
        
    }

 return 0;
}