板子———Dinic算法

//#include<bits/stdc++.h>
#include<algorithm>
#include <iostream>
#include   <fstream>
#include  <cstdlib>
#include  <cstring>
#include  <cassert>
#include   <cstdio>
#include   <vector>
#include   <string>
#include    <cmath>
#include    <queue>
#include    <stack>
#include      <set>
#include      <map>
using namespace std;
#define P(a,b,c) make_pair(a,make_pair(b,c))
#define rep(i,a,n) for (int i=a;i<=n;i++)
#define per(i,a,n) for (int i=n;i>=a;i--)
#define CLR(vis) memset(vis,0,sizeof(vis))
#define MST(vis,pos) memset(vis,pos,sizeof(vis))
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
typedef pair<int,pair<int,int> >pii;
typedef long long ll;
typedef unsigned long long ull;
const ll mod = 1000000007;
ll gcd(ll a, ll b) {
	return b ? gcd(b, a%b) : a;
}
template<class T>inline void gmax(T &A, T B) {
	(A<B)&&(A=B);//if(B>A)A=B;
}
template<class T>inline void gmin(T &A, T B) {
	(A>B)&&(A=B);//if(B<A)A=B;
}
template <class T>
inline bool scan_d(T &ret) {
	char c;
	int sgn;
	if(c=getchar(),c==EOF) return 0; //EOF
	while(c!='-'&&(c<'0'||c>'9')) c=getchar();
	sgn=(c=='-')?-1:1;
	ret=(c=='-')?0:(c-'0');
	while(c=getchar(),c>='0'&&c<='9') ret=ret*10+(c-'0');
	ret*=sgn;
	return 1;
}
inline void outt(int x) {
	if(x>9) outt(x/10);
	putchar(x%10+'0');
}
const int inf=1<<29,N=50010,M=300010;
int head[N],ver[N],edge[N],Next[N],d[N];
int n,m,s,t,tot,maxflow;
queue<int>q;
void add(int x,int y,int z)
{
	ver[++tot]=y;edge[tot]=z;Next[tot]=head[x];head[x]=tot;
	ver[++tot]=x;edge[tot]=0;Next[tot]=head[y];head[y]=tot;
}
bool bfs()//在残量网络上构造分层图 
{
	memset(d,0,sizeof(d));
	while(q.size())q.pop();
	q.push(s);d[s]=1;
	while(q.size())
	{
		int x=q.front();q.pop();
		for(int i=head[x];i;i=Next[i])
		    if(edge[i]&&!d[ver[i]])
		    {
		    	q.push(ver[i]);
		    	d[ver[i]]=d[x]+1;
		    	if(ver[i]==t)return 1;
			}
	}
	return 0;
}
int dinic(int x,int flow)//在当前分层图上增广 
{
	if(x==t)return flow;
	int rest=flow,k;
	for(int i=head[x];i;i=Next[i])
	    if(edge[i]&&d[ver[i]]==d[x]+1)
	    {
	    	k=dinic(ver[i],min(rest,edge[i]));
	    	if(!k)d[ver[i]]=0;
	    	edge[i]-=k;
	    	edge[i^1]+=k;
	    	rest-=k;
		}
	return flow-rest;
}
int main()
{
	
	cin>>n>>m;
	cin>>s>>t;//源点、汇点
	memset(head,0,sizeof(head));
	tot=1;
	for(int i=1;i<=m;i++)
	{
		int x,y,c;scanf("%d%d%d",&x,&y,&c);
		add(x,y,c);
	}
	int flow=0;
	while(bfs())
		while(flow=dinic(s,inf))maxflow+=flow;
	cout<<maxflow<<endl;
}