1 #include<iostream>
  2 #include<cstring>
  3 #include<cstdio>
  4 #include<queue>
  5 using namespace std;
  6 inline int read(){
  7     int sum(0);
  8     char ch(getchar());
  9     for(;ch<'0'||ch>'9';ch=getchar());
 10     for(;ch>='0'&&ch<='9';sum=sum*10+(ch^48),ch=getchar());
 11     return sum;
 12 }
 13 struct edge{
 14     int e,n,w;
 15 }a[400005];
 16 int pre[100005],tot;
 17 inline void insert(int s,int e,int w){
 18     a[tot].e=e;
 19     a[tot].w=w;
 20     a[tot].n=pre[s];
 21     pre[s]=tot++;
 22 }
 23 int n,m;
 24 int ed;
 25 int S(0),T;
 26 int ans(0),inf(0x7fffffff);
 27 int dis[100005];
 28 inline bool bfs(int s,int t){
 29     memset(dis,0,sizeof(dis));
 30     dis[s]=1;
 31     queue<int>q;
 32     q.push(s);
 33     while(!q.empty()){
 34         int k(q.front());
 35         q.pop();
 36         for(int i=pre[k];i!=-1;i=a[i].n){
 37             int e(a[i].e);
 38             if(!dis[e]&&a[i].w){
 39                 dis[e]=dis[k]+1;
 40                 q.push(e);
 41                 if(e==t)
 42                     return true;
 43             }
 44         }
 45     }
 46     return false;
 47 }
 48 inline int my_min(int a,int b){
 49     return a<b?a:b;
 50 }
 51 inline int dfs(int now,int flow){
 52     if(now==T)
 53         return flow;
 54     int tmp(flow),f;
 55     for(int i=pre[now];i!=-1;i=a[i].n){
 56         int e(a[i].e);
 57         if(dis[e]==dis[now]+1&&tmp&&a[i].w){
 58             f=dfs(e,my_min(tmp,a[i].w));
 59             if(!f){
 60                 dis[e]=0;
 61                 continue;
 62             }
 63             a[i].w-=f;
 64             a[i^1].w+=f;
 65             tmp-=f;
 66         }
 67     }
 68     return flow-tmp;
 69 }
 70 inline void dinic(int s,int t){
 71     while(bfs(s,t))
 72         ans+=dfs(s,inf);
 73 }
 74 int dfn[100005],low[100005],bl[100005],stack[100005];
 75 int qlt,cnt,top;
 76 bool vis[100005];
 77 inline void tarjan(int u){
 78     dfn[u]=low[u]=++cnt;
 79     stack[++top]=u;
 80     vis[u]=1;
 81     for(int i=pre[u];i!=-1;i=a[i].n)
 82         if(a[i].w){
 83             int e(a[i].e);
 84             if(!dfn[e]){
 85                 tarjan(e);
 86                 low[u]=my_min(low[u],low[e]);
 87             }
 88             else
 89                 if(vis[e])
 90                     low[u]=my_min(low[u],dfn[e]);
 91         }
 92     if(low[u]==dfn[u]){
 93         qlt++;
 94         while(1){
 95             int tmp(stack[top--]);
 96             vis[tmp]=0;
 97             bl[tmp]=qlt;
 98             if(tmp==u)
 99                 break;
100         }
101     }
102 }
103 inline int gg(){
104     freopen("bloodsail.in","r",stdin);
105     freopen("bloodsail.out","w",stdout);
106     memset(pre,-1,sizeof(pre));
107     n=read(),m=read();
108     ed=n>>1;
109     T=n+1;
110     for(int i=1;i<=m;i++){
111         int x(read()),y(read());
112         insert(x,y,1),insert(y,x,0);
113     }
114     for(int i=1;i<=ed;i++)
115         insert(S,i,1),insert(i,S,0),insert(i+ed,T,1),insert(T,i+ed,0);
116     dinic(S,T);//cout<<ans<<endl;
117     for(int i=0;i<=n+1;i++)
118         if(!dfn[i])
119             tarjan(i);
120     for(int i=1;i<=ed;i++)
121         for(int j=pre[i];j!=-1;j=a[j].n)
122             if(!a[j].w&&bl[i]==bl[a[j].e]&&a[j].e)
123                 ans--;
124     printf("%d",ans);
125     return 0;
126 }
127 int K(gg());
128 int main(){;}