#include <iostream>

 #include<cstdio>

 #include<cstring>

 #include<algorithm>

 #include<stdlib.h>

 #include<vector>

 #include<cmath>

 using namespace std;

 #define N 100010

 vector<int>d[N];

 int dp[N][],g;

 struct node

 {

     int u,v;

 }p[N];

 int dfs(int u,int v,int f)

 {

     if(dp[v][f]!=-)

     return dp[v][f];

     int i;

     int s[][] = {};

     int flag =,x=-;

     for(i =  ; i < d[v].size() ; i++)

     {

         int tv = d[v][i];

         if(tv==u) continue;

         flag = ;

         int s1 = dfs(v,tv,);

         if(f)

         {

             s[(i+)%][] = s[i%][]+s1;

         }

         else

         {

             int s2 = dfs(v,tv,)+;

             s[(i+)%][] = s[i%][]+s1;

             if(s[i%][]+s1<s[i%][]+s2)

             {

                 s[(i+)%][] = s[i%][]+s2;

                 x = tv;

             }

             else

             s[(i+)%][] = s[i%][]+s1;

         }

     }

     if(!flag)

     {

         return dp[v][f] = ;

     }

     if(x!=-)

     {

         g++;

         p[g].u = v;

         p[g].v = x;

     }

     int maxz = ;

     for(i =  ; i <  ; i++)

     maxz = max(maxz,max(s[][i],s[][i]));

     return dp[v][f] = maxz;

 }

 int main()

 {

     int i,n,m;

     while(cin>>n>>m)

     {

         memset(dp,-,sizeof(dp));

         for(i =  ; i <= n ;i++)

         d[i].clear();

         for(i = ; i <= m ;i++)

         {

             int u,v;

             cin>>u>>v;

             d[u].push_back(v);

             d[v].push_back(u);

         }

         dfs(-,,);

         cout<<dp[][]<<endl;

         for(i = ; i <= g ; i++)

         cout<<p[i].u<<" "<<p[i].v<<endl;

     }

     return ;

 }