#include <stdio.h>

int main() {

int first_input = 0;

while(scanf("%d", &first_input) != EOF) {

int everything_ok = 0;
int number_of_iterations = 0;
if(first_input == 1) {
//printf("0\n");
everything_ok = 1;
}

int numbers[first_input];
for(int i = 0; i < first_input; i++) {
scanf("%d", &numbers[i]);
//printf("%d ", numbers[i]);
}

//printf("\n");


int first_index = 0;


while(!everything_ok) {
	for(int i = 0; i < first_input; i++) {
		if (numbers[i] != i + 1) {
			everything_ok = 0;
			break;
		}

		if(i + 1 == first_input) {
			everything_ok = 1;
		}

	}

	
	if(everything_ok == 1) {
		everything_ok = 0;
		break;
	}

	if(numbers[first_index] == first_index + 1) {
		first_index++;
	}

	int first = numbers[first_index];
	int temp = numbers[first_index];
	numbers[first_index] = numbers[temp - 1];
	numbers[temp - 1] = temp;

	number_of_iterations++;

	/*
	temp = numbers[first_index]
			numbers[first_index] = numbers[first - 1]
			numbers[first - 1] = temp
			#print("AFTER = numbers[0] = ", numbers[first_index], ", numbers[first - 1] = ", numbers[first - 1])
			
					
			number_of_iterations += 1
	*/

}

printf("%d\n", number_of_iterations);

}


return 0;
}