rt，写的二分图最大匹配

#include<bits/stdc++.h>
#define int long long
#pragma GCC optimeze(2)
#pragma GCC optimeze(3)
#define lowbit(x) (x&(-x))
#define fi first	
#define PII pair<int,int> 
#define se second 
#define pu(x) push_back(x)
using namespace std;
const int N=10005;
const int M=1e6+5;
int read() {
	int x=0,flag=1;
	char ch=0;
	while(ch<'0'||ch>'9') {
		if(ch=='-')flag=-1;
		ch=getchar();
	}
	while(ch>='0'&&ch<='9') {
		x=(x<<1)+(x<<3)+ch-'0';
		ch=getchar();
	}
	return flag*x;
}
void write(int x) {
  if(x<0)putchar('-'),x=-x; 
  static int sta[35];
  int top = 0;
  do {
    sta[top++] = x % 10, x /= 10;
  } while (x);
  while (top) putchar(sta[--top] + 48);
}
int n,head[N],ne[M*2],ver[M*2],tot,ma[M],bj[M];
void add(int x,int y){
	ver[++tot]=y,ne[tot]=head[x],head[x]=tot;
}
bool match(int x){
//	cout<<"TEST "<<x<<endl; 
	for(int i=head[x];i;i=ne[i]){
		int to=ver[i];
//		cout<<to<<endl;
		if(bj[to]!=x){
			bj[to]=x;
			if(!ma[to]||match(ma[to])){
				ma[to]=x;
				return true;
			}
		}
	}
	return false;
}
signed main() {
	n=read();
	for(int i=1;i<=n;i++){
		int u=read(),v=read();
		add(u,i),add(v,i);
	}
	for(int i=1;i<=10000;i++){
		if(!match(i)){
			cout<<i-1;
			return 0;
		}
	}
	cout<<10000;
	return 0;
}