#include <bits/stdc++.h>
using namespace std;

const int kNmax = 100005;

class Task {
public:
    void solve() {
        read_input();
        print_output(get_result());
    }

private:
    int n;
    int m;
    int source;
    vector<int> adj[kNmax];

    void read_input() {
        ifstream fin("dfs.in");
        fin >> n >> m >> source;
        for (int i = 1, x, y; i <= m; i++) {
            fin >> x >> y;
            adj[x].push_back(y);
            adj[y].push_back(x);
        }
        fin.close();
    }

    int computeDFS() {
        // Mark nodes as not visited
        vector<int> visited(n + 1, 0);
        int connected_comp = 1;

        // Recursively visit every node
        for (int i = 1; i <= n; ++i) {
            if (!visited[i]) {
                dfs(i, visited, connected_comp);
                connected_comp++;
            }
        }

        return connected_comp - 1;
    }

    void dfs(int node, vector<int> &visited, int &connected_comp) {
        visited[node] = 1;
        for (auto &it : adj[node]) {
            if (!visited[it]) {
                dfs (it, visited, connected_comp);
            }
        }
    }

    int get_result() {
       return computeDFS();
    }

    void print_output(int result) {
        ofstream fout("dfs.out");
        fout<<result;
        fout.close();
    }
};

int main() {
    Task *task = new Task();
    task->solve();
    delete task;
    return 0;
}