858.cpp

#include <iostream>
#include <cmath>
#include <cstdio>
#include <vector>

using namespace std;

const char opened = 2;
const char marked = 1;
const char untouched = 0;

int n, tmp, *prev, count;
char *vis;
vector<int> *a;

void ds(int k);

int main(){

    cin >> n;
    a = new vector<int>[n];
    prev = new int[n];
    vis = new char[n];
    count = 0;

    for (int i = 0; i < n; i++){
        cin >> tmp;
        a[--tmp].push_back(i);
        prev[i] = tmp;
        vis[i] = untouched;
    }

    for (int i = 0; i < n; i++){
        if (vis[i] == opened)
            continue;
        int j = i;
        while (vis[prev[j]] == untouched){
            vis[j] = marked;
            j = prev[j];
        }
        ds(j);
        count++;
    }

    cout << count << endl;

    delete [] a;
    delete [] vis;
    delete [] prev;

    return 0;
}

void ds(int k){
    vis[k] = opened;
    for (int i = 0; i < a[k].size(); i++){
        if (vis[a[k][i]] == opened)
            continue;
        ds(a[k][i]);
    }
}