套EK模板
#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#include <stack>
#include <map>
#include <cmath>
#include <algorithm>
#define inf 0x3f3f3f3f
#define SI(a) scanf("%d",&a)
#define set0(a) memset(a,0,sizeof(a))
#define setMo(a) memset(a,-1,sizeof(a))
typedef long long ll;
const int mod = 998244353;
const int maxn = 2e5+10;
using namespace std;
struct Edge{
int from,to,cap,flow;
Edge(int u,int v,int c,int f):from(u),to(v),cap(c),flow(f){
}
};
//基于BFS的增广路算法
int n,m,u,v,s,t;
vector<Edge>edges;//边集
vector<int>G[maxn];//邻接表
int a[maxn];//可改进量
int p[maxn];//最短路上p的入弧编号
int vis[maxn];
void init(int n)
{
for(int i = 0;i <= n+3;i++)
G[i].clear();
edges.clear();
}
void AddEdge(int from,int to,int cap)
{
edges.push_back(Edge(from,to,cap,0));
edges.push_back(Edge(to,from,0,0));
m = edges.size();
G[from].push_back(m-2);
G[to].push_back(m-1);
}
int MaxFlow(int s,int t)
{
int flow = 0;
for(;;)
{
set0(a);
queue<int>q;
q.push(s);
a[s] = inf;
while(!q.empty())
{
int x = q.front();
q.pop();
for(int i = 0;i < (int)G[x].size();i++)
{
Edge &e = edges[G[x][i]];
//cout<<2<<endl;
if(!a[e.to]&&e.cap > e.flow){
p[e.to] = G[x][i];
a[e.to] = min(a[x],e.cap-e.flow);
q.push(e.to);
//cout<<1<<endl;
}
}
if(a[t])break;
}
if(!a[t])break;
for(int u = t;u != s;u = edges[p[u]].from)
{
edges[p[u]].flow += a[t];
edges[p[u]^1].flow -= a[t];
}
flow += a[t];
}
return flow;
}
int main()
{
while(cin>>n>>m){
s=0,t=n+1;
//cout<<s<<" "<<t<<endl;
init(t);
set0(vis);
int u,v;
while(cin>>u>>v)
{
AddEdge(u,v,1);//能搭配的正副驾驶员加边
if(!vis[u])
{
AddEdge(s,u,1);vis[u] = 1;}
if(!vis[v])
{
AddEdge(v,t,1);vis[v] = 1;}
}
cout<<MaxFlow(s,t)<<endl;
}
}