codeforces 192b

link: http://codeforces.com/contest/330/problem/B I think the problem is hard at first. However, when you think deep in it you will find it is so easy.

/*
ID: zypz4571
LANG: C++
TASK: 192b.cpp
 */

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <cctype>
#include <algorithm>
#include <queue>
#include <deque>
#include <queue>
#include <list>
#include <map>
#include <set>
#include <vector>
#include <utility>
#include <functional>
#include <fstream>
#include <iomanip>
#include <sstream>
#include <numeric>
#include <cassert>
#include <ctime>

#define INF 0x3f3f3f3f
#define REP(i, n) for(int i=0;i<int(n);++i)
#define FOR(i, a, b) for(int i=int(a);i<int(b);++i)
#define DWN(i, b, a) for(int i=int(b-1);i>=int(a);--i)
#define REP_1(i, n) for(int i=1;i<=int(n);++i)
#define mid int m=(l+r)/2
using namespace std;
int main ( int argc, char *argv[] )
{
#ifndef ONLINE_JUDGE
freopen("in.txt", "r", stdin);
#endif
    int n, m; cin >> n >> m;
    multiset<int> rp;
    int a, b;
    REP (i, m) {
        cin >> a >> b;
        rp.insert(a); rp.insert(b);
    }
    int tmp;
    FOR(i, 1, n+1) {
        if (rp.count(i) == 0) {
            tmp = i; break;
        }
    }
    cout <<n-1<<endl;
    FOR (i, 1, n+1) {
        if (i != tmp) {
            cout << min(tmp, i) <<' '<<max(tmp,i)<<endl;
        }
    }
        return EXIT_SUCCESS;
}                /* ----------  end of function main  ---------- */

It seems that I can not use STL very skillfully.