1 #include <iostream>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <cstdio>
 5 
 6 using namespace std;
 7 const int MAX = 210;
 8 int father[MAX],a[MAX];
 9 int g[MAX][MAX],vis[MAX],link[MAX];
10 int n,m;
11 int find_father(int x)
12 {
13     if(x == father[x])
14         return x;
15     int t = find_father(father[x]);
16     a[x] = (a[father[x]] + a[x]) % 2;
17     return father[x] = t;
18 }
19 int dfs(int x)
20 {
21     for(int i = 1; i <= n; i++)
22     {
23         if(vis[i] == 0 && g[x][i])
24         {
25             vis[i] = 1;
26             if(link[i] == 0 || dfs(link[i]))
27             {
28                 link[i] = x;
29                 return true;
30             }
31         }
32     }
33     return false;
34 }
35 int main()
36 {
37     while(scanf("%d%d",&n,&m) != EOF)
38     {
39         for(int i = 0; i <= n; i++)
40         {
41             father[i] = i;
42             a[i] = 0;
43         }
44         memset(g,0,sizeof(g));
45         memset(link,0,sizeof(link));
46         int flag = 0,ans = 0;
47         while(m--)
48         {
49             int x,y,fx,fy;
50             scanf("%d%d",&x,&y);
51             g[x][y] = g[y][x] = 1;
52             fx = find_father(x);
53             fy = find_father(y);
54             if(fx != fy)
55             {
56                 father[fy] = fx;
57                 if(a[x] == 0)
58                 {
59                     a[fy] = 1 - a[y];
60                 }
61                 else
62                     a[fy] = a[y];
63             }
64             else
65             {
66                 if(a[x] == a[y])
67                 {
68                     flag = 1;
69                 }
70             }
71         }
72         if(flag)
73         {
74             printf("No\n");
75         }
76         else
77         {
78             for(int i = 1; i <= n; i++)
79             {
80                 memset(vis,0,sizeof(vis));
81                 if(dfs(i))
82                     ans++;
83             }
84             printf("%d\n",ans/2);
85         }
86     }
87 
88     return 0;
89 }