#include <bits/stdc++.h>

using namespace std;

int main()
{
    iostream::sync_with_stdio(0);
    cin.tie(0);
    vector<vector<int>> fa;
    int n,m,apa,be1,be2,szint;
    vector<int> q;
    cin >> n>>m>>apa;
    for(int i = 0; i<=n+1;i++){fa.push_back(q);}
    //cout <<"fa:"<< fa.size()<<endl;
    vector<int> volte;
    volte.assign(n+1,-10);
    vector<pair<int,int>> kimenet;
    for(int i =0;i<m;i++)
    {
        cin >> be1 >>be2;
        fa[be1].push_back(be2);
        fa[be2].push_back(be1);
    }
    vector<queue<int>> valami;
    queue<int> qqqqqq;
    for(int i = 0; i < n+1; i++) valami.push_back(qqqqqq);
    int mostani=apa;
    pair<int,int>temp;
    szint = 0;
    volte[apa] = -1;
    for(int x : fa[apa])
    {
        valami[0].push(x);
        volte[x] = 0;
    }
    //cout <<"hiii"<<endl;
    bool alma = false;
while(!alma)
{
    alma = true;
    //cout << "kulso"<<endl;
    while(!valami[szint].empty())
    {
        alma = false;
        //cout << "belso"<<endl;
        mostani = valami[szint].front();
        valami[szint].pop();
        //cout << "mostani:" << mostani <<endl;
        //cout << "szint:" << szint <<endl;
        for(int x : fa[mostani])
        {
            //cout <<"x:"<<x<<endl;
            //cout<<"voltex"<<volte[x]<<" voltemost"<<volte[mostani]<<endl;
            if(volte[x] == volte[mostani]-1)
            {
                temp.first = x;
                temp.second = mostani;
                kimenet.push_back(temp);
            }
            else if(volte[x]==-10)
            {
                valami[szint+1].push(x);
                volte[x] = szint+1;
            }
        }
    }
    szint++;
}
    cout << kimenet.size()<<endl;
    for(pair<int,int> x: kimenet) {cout << x.first << " "<<x.second<<endl;}
}