#include <vector>
#include <string>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <queue>
#include <bitset>
#include <stack>
#include <list>
#include <numeric>
#include <algorithm>
#include <random>
#include <chrono>
#include <cstdio>
#include <fstream>
#include <iostream>
#include <sstream>
#include <iomanip>
#include <climits>
#include <cctype>
#include <cmath>
#include <ctime>
#include <cassert>
using namespace std;
#define ULL unsigned long long
#define LL long long
#define PII pair <int, int>
#define VB vector <bool>
#define VI vector <int>
#define VLL vector <LL>
#define VD vector <double>
#define VS vector <string>
#define VPII vector <pair <int, int> >
#define VVI vector < VI >
#define VVB vector < VB >
#define SI set < int >
#define USI unordered_set <int>
#define MII map <int, int>
#define UMII unordered_map <int, int>
#define MS multiset
#define US unordered_set
#define UM unordered_map
#define UMS unordered_multiset
#define UMM unordered_multimap
#define FORN(i, n) for(int i = 0; i < (n); ++i)
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define SZ size()
#define BG begin()
#define EN end()
#define CL clear()
#define X first
#define Y second
#define RS resize
#define PB push_back
#define MP make_pair
#define ALL(x) x.begin(), x.end()
#define INS insert
#define ER erase
#define CNT count
int n, m, source;
VVI g;
VI dist;
void bf()
{
dist.RS(n + 1, -1);
queue<int> fifo;
fifo.push(source);
dist[source] = 0;
while (!fifo.empty())
{
int node = fifo.front();
fifo.pop();
for (int next : g[node])
if (dist[next] == -1)
{
dist[next] = dist[node] + 1;
fifo.push(next);
}
}
}
int main()
{
cin >> n >> m >> source;
g.RS(n + 1);
FOR(i, 1, m)
{
int x, y;
cin >> x >> y;
g[x].PB(y);
g[y].PB(x);
}
bf();
VPII sol;
FOR(i, 1, n)
for (int j : g[i])
if (dist[j] == dist[i] + 1) sol.PB({i, j});
cout << sol.SZ << "\n";
for (auto [x, y] : sol) cout << x << " " << y << "\n";
return 0;
}