1 #include <iostream>
 2 #include <set>
 3 #include <cstdio>
 4 #include <cstring>
 5 #include <vector>
 6 using namespace std;
 7 
 8 const int maxn = 205;
 9 const int INF = 1000000000;
10 int n;
11 
12 int col[maxn];
13 vector<int> G[maxn];
14 bool is_bi(int u) {
15     for(int i = 0; i < G[u].size(); i++) {
16         int v = G[u][i];
17         if(col[u] == col[v]) return false;
18         if(!col[v]) {
19             col[v] = 3 - col[u];
20             if(!is_bi(v)) return false;
21         }
22     }
23     return true;
24 }
25 bool check() {
26     for(int i = 1; i <= n; i++) {
27         if(G[i].size()) {
28             memset(col, 0, sizeof(col));
29             col[i] = 1;
30             if(!is_bi(i)) return false;
31         }
32     }
33     return true;
34 }
35 
36 int vis[maxn];
37 int Left[maxn];
38 int Link[maxn];
39 vector<int> V[maxn];
40 bool Find(int u) {
41     for(int i = 0; i < V[u].size(); i++) {
42         int v = V[u][i];
43         if(!vis[v]) {
44             vis[v] = 1;
45             if(Link[v] == -1 || Find(Link[v])) {
46                 Link[v] = u;
47                 return true;
48             }
49         }
50     }
51     return false;
52 }
53 int solve() {
54     int cnt = 0;
55     memset(Link, -1, sizeof(Link));
56     for(int i = 1; i <= n; i++) {
57         if(V[i].size()) {
58             memset(vis, 0, sizeof(vis));
59             if(Find(i)) cnt++;
60         }
61     }
62     return cnt;
63 }
64 
65 int main() {
66     int m;
67     int u, v;
68     while(EOF != scanf("%d %d",&n, &m)) {
69         for(int i = 0; i <= n; i++) {
70             G[i].clear();
71             V[i].clear();
72         }
73         while(m--) {
74             scanf("%d %d",&u, &v);
75             G[u].push_back(v);
76             G[v].push_back(u);
77             V[u].push_back(v);
78         }
79         if(!check()) {
80             puts("No");
81             continue;
82         }
83         printf("%d\n",solve()) ;
84     }
85     return 0;
86 }