1 #include
     
       2 #include
      
        3 #include
       
         4 #include
        
          5 #define N 505 6 using namespace std; 7  8 int g[N][N]; 9 int n, m;10 int vis[N], linker[N];11 bool dfs(int u){12    for(int i=1; i<=n; ++i)13       if(g[u][i] && !vis[i]){14           vis[i]=1;15           if(!linker[i] || dfs(linker[i])){16               linker[i]=u;17               return true;              18           }19       }20    return false;21 }22 23 int main(){24    while(scanf("%d%d", &n, &m) && (n||m)){25        memset(g, 0, sizeof(g));26        while(m--){27           int u, v;28           scanf("%d%d", &u, &v);29           g[u][v]=1;           30        }                    31        for(int k=1; k<=n; ++k)32           for(int i=1; i<=n; ++i)33              for(int j=1; j<=n; ++j)34                if(!g[i][j])35                   g[i][j]=g[i][k]&&g[k][j];36        memset(linker, 0, sizeof(linker));37        int ans=0;38        for(int i=1; i<=n; ++i){39            memset(vis, 0, sizeof(vis));40            if(dfs(i))  ++ans;        41        }42        printf("%d\n", n-ans);43    }44    return 0;    45 }