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

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
	int n, m, c;
    cin >> n >> m >> c;
    vector<vector<int>> g(n + 1);
    for (int i = 0; i < m; i ++) {
        int u, v; cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    queue<int> q;
    q.push(c);
    vector<int> dist(n + 1, 10000000);
    vector<bool> done(n + 1);
    dist[c] = 0;
    set<pair<int, int>> ans;
    while(!q.empty()) {
        int u = q.front();
        q.pop();
        done[u] = true;
        for (int v : g[u]) {
            if (dist[v] >= dist[u] + 1) {
                dist[v] = dist[u] + 1;
                ans.insert({u, v});
            }
            if (!done[v]) q.push(v);
        }
    }
    cout << ans.size() << "\n";
    for (auto[x, y] : ans) cout << x << " " << y << "\n";
}