#include <stdio.h>
#include <vector>
#include <queue>

using namespace std;

#define maxn 510
#define inf 2000000000
#define ll long long

int N, M, S, D;
int Drum;
vector<int> A[maxn];
vector<int> Dist, T;
queue<int> Q;
int C[maxn][maxn], F[maxn][maxn], Cost[maxn][maxn];
vector<bool> in_queue;

int BellmanFord()
{
	int x;
	vector<int> :: iterator it;
	
	in_queue.resize(N + 1);
	fill(in_queue.begin(), in_queue.end(), 0);
	Dist.resize(N + 1);
	fill(Dist.begin(), Dist.end() , inf);
	T.resize(N + 1);
	fill(T.begin(), T.end() , -1);

	Dist[S] = 0;
	Q.push(S);

	while (!Q.empty())
	{		
		x = Q.front();
		Q.pop();
		in_queue[x] = 0;

		for (it = A[x].begin(); it != A[x].end() ; it++)
			if (C[x][*it] > F[x][*it] && Dist[x]+Cost[x][*it] < Dist[*it])
			{
				Dist[*it] = Dist[x] + Cost[x][*it];
				T[*it] = x;
				if(!in_queue[*it])
				{
					in_queue[*it] = 1;
					Q.push(*it);
				}
			}
	}
	
	if (Dist[D] != inf) 
	{
		int Vmin = inf;
		Drum = 1;

		for (int i = D; i != S; i = T[i]) 
			Vmin = min(Vmin, C[T[i]][i] - F[T[i]][i]);

		for (int i = D; i != S; i = T[i]) 
		{
			F[T[i]][i] += Vmin;
			F[i][T[i]] -= Vmin;
		}

		return Vmin * Dist[D];
	}

	return 0;
}

ll Flux()
{
	ll Rez = 0;
	Drum = 1;

	while (Drum)
	{
		Drum = 0;
		Rez += BellmanFord();
	}

	return Rez;
}

int main()
{
	freopen("fmcm.in", "r", stdin);
	freopen("fmcm.out", "w", stdout);

	int x, y, z, cap;

	scanf("%d %d %d %d ", &N, &M, &S, &D);

	for (int i = 1; i <= M; i++)
	{
		scanf("%d %d %d %d ", &x, &y, &cap, &z);
		A[x].push_back(y);
		A[y].push_back(x);
		C[x][y] = cap;
		Cost[x][y] = z;
		Cost[y][x] = -z;
	}

	printf("%lld\n", Flux());

	return 0;
}