#include <stdio.h>
#include <stdlib.h>



void exchange(int *a, int *b){
	int x = *a;
	*a = *b;
	*b = x;
}

int main(){

	int *n;
	int N;
	int i;
	int last;
	int count;
	//int x;


	while(scanf("%d", &N) > 0){
		count = 0;
		n = (int*)malloc(N*sizeof(int));
		for(i = 0; i < N; i++){
			scanf("%d", n + i);
			n[i]--;
		}
		
		i = 0;

		while(n[i] == i){
			i++;
		}
		if(i > N-1){
			printf("0\n");
			continue;
		}

		last = i;

		while(1){
			if(last == n[n[last]]){

				exchange(n + last, n + n[last]);
				count++;
				while((last < N)&&(n[last] == last)){
					last++;
				}
				if(last > N - 1){
					printf("%d\n", count);
					break;
				}
			}else {

				i = last;
				while ((i < N)&&((n[n[i]] != i)||(i==n[i]))){
					i++;
				}
				//printf("%d %d %d \n", i, n[i], n[n[i]]);
					if(i > N - 1){
					exchange(&(n[last]), &(n[n[last]]));
				}else{
				//	printf("%d %d %d %d\n", n[0], n[1], n[2], n[3]);
					exchange(n + i, n + n[i]);
				}
				count++;
			}
		}									
	}



	return 0;
}