1 #include <iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<stdlib.h>
 6 #include<vector>
 7 #include<cmath>
 8 using namespace std;
 9 #define N 100010
10 vector<int>d[N];
11 int dp[N][3],g;
12 struct node
13 {
14     int u,v;
15 }p[N];
16 int dfs(int u,int v,int f)
17 {
18     if(dp[v][f]!=-1)
19     return dp[v][f];
20     int i;
21     int s[2][2] = {0};
22     int flag =0,x=-1;
23     for(i = 0 ; i < d[v].size() ; i++)
24     {
25         int tv = d[v][i];
26         if(tv==u) continue;
27         flag = 1;
28         int s1 = dfs(v,tv,0);
29         if(f)
30         {
31             s[(i+1)%2][0] = s[i%2][0]+s1;
32         }
33         else
34         {
35             int s2 = dfs(v,tv,1)+1;
36             s[(i+1)%2][0] = s[i%2][0]+s1;
37             if(s[i%2][1]+s1<s[i%2][0]+s2)
38             {
39                 s[(i+1)%2][1] = s[i%2][0]+s2;
40                 x = tv;
41             }
42             else
43             s[(i+1)%2][1] = s[i%2][1]+s1;
44         }
45     }
46     if(!flag)
47     {
48         return dp[v][f] = 0;
49     }
50     if(x!=-1)
51     {
52         g++;
53         p[g].u = v;
54         p[g].v = x;
55     }
56     int maxz = 0;
57     for(i = 0 ; i < 2 ; i++)
58     maxz = max(maxz,max(s[0][i],s[1][i]));
59     return dp[v][f] = maxz;
60 }
61 int main()
62 {
63     int i,n,m;
64     while(cin>>n>>m)
65     {
66         memset(dp,-1,sizeof(dp));
67         for(i = 0 ; i <= n ;i++)
68         d[i].clear();
69         for(i = 1; i <= m ;i++)
70         {
71             int u,v;
72             cin>>u>>v;
73             d[u].push_back(v);
74             d[v].push_back(u);
75         }
76         dfs(-1,1,0);
77         cout<<dp[1][0]<<endl;
78         for(i = 1; i <= g ; i++)
79         cout<<p[i].u<<" "<<p[i].v<<endl;
80     }
81     return 0;
82 }