二分圖最大匹配（模板）

//#include<bits/stdc++.h>
#include<stdio.h>
#include<algorithm>
#include<iostream>
#include<string.h>
#define LL long long
#define Max 100005
const LL mod=1e9+7;
const LL LL_MAX=9223372036854775807;
using namespace std;
int road[505][10005],used[Max];
int match[Max];
int n,k;
bool dfs(int x){
    for(int i=1;i<=n;i++)
    if(!used[i] && road[x][i]){
        used[i]=1;
        if(!match[i] || dfs(match[i])){
            match[i]=x;
            return 1;
        }
    }
    return 0;
}
int main()
{
    scanf("%d%d",&n,&k);
    int x,y;
    for(int i=0;i<k;i++){
        scanf("%d%d",&x,&y);
        road[x][y]=1;
    }
    int ans=0;
    for(int i=1;i<=n;i++){
        memset(used,0,sizeof(used));
        if(dfs(i))
            ans++;
    }
    printf("%d\n",ans);
    return 0;
}