22_3

#include <iostream>
#include <vector>

using namespace std;

class Stack {
private:
    vector<int> data;

public:
    void push(int value) {
        data.push_back(value);
    }

    void pop() {
        if (!data.empty()) {
            data.pop_back();
        }
    }

    int top() {
        if (!data.empty()) {
            return data.back();
        }
        return -1;
    }

    bool isEmpty() {
        return data.empty();
    }
};

class Cycle {
public:
    int start;
    int finish;

    Cycle(int s, int f) {
        start = s;
        finish = f;
    }
};

class Graph {
private:
    vector<Cycle> cycles;
    vector<bool> visited;

    // Поиск в глубину - ищет и считает циклы
    void dfs(int node, int& cycleCount) {
        visited[node] = true;
        int next = cycles[node].finish - 1;
        if (!visited[next]) {
            dfs(next, cycleCount);
        } else {
            cycleCount++;
        }
    }

public:
    Graph(int N) {
        visited.resize(N, false);
    }

    ~Graph() {
    }
    void addCycle(int start, int finish) {
        Cycle newCycle(start, finish);
        cycles.push_back(newCycle);
    }

    int countDisjointCycles() {
        int cycleCount = 0;
        for (int i = 0; i < cycles.size(); ++i) {
            if (!visited[i]) {
                dfs(i, cycleCount);
            }
        }
        return cycleCount;
    }
};

int main() {
    int N;
    cout << "Число: ";
    cin >> N;
    Graph graph(N);

    cout << "Старт и начало: " << endl;
    for (int i = 0; i < N; ++i) {
        int start, finish;
        cin >> start >> finish;
        graph.addCycle(start, finish);
    }
    cout << "Число непересекающихся" << graph.countDisjointCycles() << endl;
    return 0;
}