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, , n+) {
         if (rp.count(i) == ) {
             tmp = i; break;
         }
     }
     cout <<n-<<endl;
     FOR (i, , n+) {
         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.