Dinic

#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<iostream>
#include<ctime>
#include<map>
#include<queue>
#include<cstdlib>
#include<string>
#include<climits>
#include<set>
#include<vector>
using namespace std;
const int maxN=1000005,maxM=1000005,oo=10000000000000000ll;
int n,m,s,t,cnt,Head[maxN],Next[maxM],W[maxM],V[maxM],Depth[maxN],cur[maxN];
void _Add(int u,int v,int w){
	cnt++;
	Next[cnt]=Head[u];
	Head[u]=cnt;
	V[cnt]=v;
	W[cnt]=w;
}
void Add_Edge(int u,int v,int w){
	_Add(u,v,w);
	_Add(v,u,0);
}
int dfs(int u,int flow){
	if(u==t){
		return flow;
	}
	for(int& i=cur[u];i!=-1;i=Next[i]){
		if((Depth[V[i]]==Depth[u]+1)&&(W[i]!=0)){
			int di=dfs(V[i],min(flow,W[i]));
			if(di>0){
				W[i]-=di;
				W[i^1]+=di;
				return di;
			}
		}
	}
	return 0;
}
int bfs(){
	queue<int> Q;
	while(!Q.empty()){
		Q.pop();
	}
	memset(Depth,0,sizeof(Depth));
	Depth[s]=1;
	Q.push(s);
	do{
		int u=Q.front();
		Q.pop();
		for(int i=Head[u];i!=-1;i=Next[i]){
			if((Depth[V[i]]==0)&&(W[i]>0)){
				Depth[V[i]]=Depth[u]+1;
				Q.push(V[i]);
			}
		}
	}
	while(!Q.empty());
	if(Depth[t]>0){
		return 1;
	}
	return 0;
}
int Dinic(){
	int Ans=0;
	while (bfs()){
		for(int i=1;i<=n;i++){
			cur[i]=Head[i];
		}
		while(int d=dfs(s,oo)){
			Ans+=d;
		}
	}
	return Ans;
}
int main(){
	int u,v,w;
	cnt=-1;
	memset(Head,-1,sizeof(Head));
	memset(Next,-1,sizeof(Next));
	scanf("%d%d%d%d",&n,&m,&s,&t);
	for(int i=1;i<=m;i++){
		scanf("%d%d%d",&u,&v,&w);
		Add_Edge(u,v,w);
	}
	printf("%d\n",Dinic());
	return 0;
}