Dinic80pts求条

#include<bits/stdc++.h>
//#define int long long
using namespace std;
int n1,n2,n3,m1,m2;
int n,m,S,T,ans;
int head[10000010],to[10000010],nex[10000010],cnt;
int val[1000010],deep[1000010],cur[1000010];
inline void Add(int u,int v,int w){
	to[cnt]=v;
	val[cnt]=w;
	nex[cnt]=head[u];
	head[u]=cnt++;
}
queue<int> q;
inline bool bfs(){
	memset(deep,0,sizeof deep);
	while(q.size()) q.pop();
	q.push(S);
	deep[S]=1;
	while(q.size()){
		int u=q.front();
		q.pop();
		for(int i=head[u];i!=-1;i=nex[i]){
			int v=to[i];
			if(val[i]>0&&deep[v]==0){
				deep[v]=deep[u]+1;
				q.push(v);
			}
		}
	}
	return bool(deep[T]);
}
inline int dfs(int u,int f){
	if(u==T) return f;
	int use=0;
	for(int &i=cur[u];i!=-1;i=nex[i]){
		int v=to[i];
		if(val[i]>0&&deep[v]==deep[u]+1){
			int ff=dfs(v,min(f-use,val[i]));
			if(ff>0){
				val[i]-=ff;
				val[i^1]+=ff;
				use+=ff;
				if(use==f) break;
			}
		}
	}
	if(use==0) deep[u]=0;
	return use;
}
inline void Dinic(){
	while(bfs()){
		for(int i=0;i<=n;i++) cur[i]=head[i];
		ans+=dfs(S,1e9);
	}
}
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);
	memset(head,-1,sizeof(head));
	cin>>n>>m>>S>>T;
	for(int i=1;i<=m;i++){
		int x,y,s=1;
		cin>>x>>y;
		Add(x,y,s);
		Add(y,x,0);
		Add(y,x,s);
		Add(x,y,0);
	}
	Dinic();
	cout<<ans;
	return 0;
}