bzoj1143

#include<bits/stdc++.h> 
using namespace std;
const int N=105;
int n,m,x,y,l,ans,id,to[N],bz[N],zz[N*N],ne[N*N],fi[N],f[N][N];
void jb(int x,int y) 
{
    zz[++l]=y;
    ne[l]=fi[x];
    fi[x]=l;
}
int match(int x) 
{
    for (int i=fi[x];i;i=ne[i])
     if (bz[zz[i]]!=id)
      {
        bz[zz[i]]=id;
        if (!to[zz[i]]||match(to[zz[i]]))
         {
            to[zz[i]]=x;
            return 1;
         }
      }
    return 0;
}
int main() 
{
    scanf("%d%d",&n,&m);
    ans=n;
    while (m--)scanf("%d%d",&x,&y),f[x][y]=1;
    for (int k=1;k<=n;k++)
     for (int i=1;i<=n;i++)
      for (int j=1;j<=n;j++)f[i][j]=f[i][j]||f[i][k]&&f[k][j];
    for (int i=1;i<=n;i++)
     for (int j=1;j<=n;j++)
      if (f[i][j])jb(i,j);
    for (int i=1;i<=n;i++)id++,ans-=match(i);
    printf("%d",ans);
}