// Source: https://usaco.guide/general/io

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

int main() {
	int N,M,strNODE; cin >> N >> M >> strNODE;
	vector<vector<int>> v(N+1);
	for(int i = 1; i <= M; i++) {
		int a,b;
		cin >> a >> b;
		v[a].push_back(b);
		v[b].push_back(a);
	}
	vector<int> ut(N+1,-1);
	map<pair<int,int>, bool> m;
	queue<int> q;
	q.push(strNODE);
	while(!q.empty()){
		int temp=q.front();
		q.pop();
		for(int n : v[temp]){
			if(ut[n]==-1){
				ut[n]=ut[temp]+1;
				q.push(n);
			}
			if(ut[temp]==ut[n]+1)m[make_pair(n,temp)]=true;
		}
	}
	cout<<m.size()<<endl;
	for(auto ans : m){
		cout<<ans.first.second<<' '<<ans.first.first<<endl;
	}
}