#include<bits/stdc++.h>
#define FILE "read"
#define MAXN 205
#define INF 1e9
using namespace std;
typedef bitset<MAXN> Int;
struct node{int y,next,v;}e[MAXN*MAXN*2];
int n,m,S,T,len(1),Link[MAXN],level[MAXN];
Int M[MAXN];
queue<int>q;
inline int read(){
    int x=0,f=1;  char ch=getchar();
    while(!isdigit(ch))  {if(ch=='-')  f=-1;  ch=getchar();}
    while(isdigit(ch))  {x=x*10+ch-'0';  ch=getchar();}
    return x*f;
}
void insert(int x,int y,int v){
    e[++len].next=Link[x];Link[x]=len;e[len].y=y;e[len].v=v;
    e[++len].next=Link[y];Link[y]=len;e[len].y=x;e[len].v=0;
}
bool bfs(){
    memset(level,-1,sizeof(level));
    q.push(S);  level[S]=0;
    while(!q.empty()){
        int x=q.front(); q.pop();
        for(int i=Link[x];i;i=e[i].next)if(level[e[i].y]==-1&&e[i].v){
            level[e[i].y]=level[x]+1;  q.push(e[i].y);
        }
    }
    return level[T]>=0;
}
int MAXFLOW(int x,int flow){
    if(x==T)  return flow;
    int d=0,maxflow=0;
    for(int i=Link[x];i&&maxflow<flow;i=e[i].next)
        if(level[e[i].y]==level[x]+1&&e[i].v)
            if(d=MAXFLOW(e[i].y,min(e[i].v,flow-maxflow))){
                e[i].v-=d;  e[i^1].v+=d;  maxflow+=d;
            }
    if(!maxflow)  level[x]=-1;
    return maxflow;
}
int main(){
    //freopen(FILE".in","r",stdin);
    //freopen(FILE".out","w",stdout);
    n=read();  m=read();  S=0;  T=n*2+1;
    for(int i=1;i<=m;++i){
        int x=read(),y=read();
        M[x][y]=1;
    }
    for(int i=1;i<=n;++i)for(int j=1;j<=n;++j)
        if(M[i][j])M[i]|=M[j];
    for(int i=1;i<=n;++i)for(int j=1;j<=n;++j)
        if(M[i][j])insert(i,j+n,1);
    for(int i=1;i<=n;++i)insert(S,i,1);
    for(int i=1;i<=n;++i)insert(i+n,T,1);
    int ans=n,d=0;
    while(bfs()) while(d=MAXFLOW(S,INF)) ans-=d;
    printf("%d\n",ans);
    return 0;
}