#include <bits/stdc++.h>
using namespace std;
vector<int> tav;
vector<int> g[60001];
vector<pair<int,int>> good;
void bfs(int s){
    queue<int> q;
    q.push(s);
    while (!q.empty()){
        int v=q.front();
        q.pop();
        for (int edge:g[v]){
            if (tav[edge]==1e9){
                tav[edge]=tav[v]+1;
                q.push(edge);
                good.push_back({v,edge});
            }
            else{
                if (tav[edge]==tav[v]+1) good.push_back({v,edge});
            }
        }
    }
    cout<<good.size()<<endl;
    for (auto x:good) cout<<x.first<<" "<<x.second<<endl;
}
int main()
{

    vector<pair<int,int>> good;
    int n,m,k;
    cin>>n>>m>>k;
    tav.resize(n+1,1e9);
    tav[k]=0;
    for (int i=0; i<m;i++){
        int a,b;
        cin>>a>>b;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    bfs(k);

}