#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <fstream>
#include <iterator>
#include <random>
#include <assert.h>
using namespace std;

const string file = "fmcm";

const string infile = file + ".in";
const string outfile = file + ".out";

const int INF = 0x3f3f3f3f; 

//#define ONLINE_JUDGE

vector<vector<int> > Cap;
vector<vector<int> > Cost;

vector<int> prec;
vector<int> potential;
vector<int> reald;
vector<int> dist;

int MinCost;
int S;
int D;
int N;
int M;

vector<vector<int> > G;

void bellman()
{
    vector<bool> inQ(N + 1, false);
    queue<int> que;
    fill(potential.begin(), potential.end(), INF);

    que.push(S);
    potential[S] = 0;
    inQ[S] = true;

    while(que.empty() == false)
    {
        int x = que.front();
        inQ[x] = false;
        que.pop();
        for(vector<int>::iterator itr = G[x].begin();
                itr != G[x].end();
                itr++)
        {
            if(Cap[x][*itr] == 0)
                continue;
            int nod = *itr;
            int newDist = potential[x] + Cost[x][nod];
            if(potential[nod] > newDist)
            {
                potential[nod] = newDist;
                if(inQ[nod] == false)
                {
                    que.push(nod);
                    inQ[nod] = true;
                }
            }
        }
    }
}

bool dijkstra()
{
    fill(dist.begin(), dist.end(), INF);
    fill(reald.begin(), reald.end(), INF);
    priority_queue<pair<int, int>, vector<pair<int, int> >, greater<pair<int, int> > > heap;
    heap.push(make_pair(0, S));

    reald[S] = 0;
    dist[S] = 0;

    while(heap.empty() == false)
    {
        pair<int, int> c = heap.top();
        heap.pop();
        int d = c.first;
        int x = c.second;
        
        if(dist[x] != d)
            continue;

        for(vector<int>::iterator itr = G[x].begin();
                itr != G[x].end();
                itr++)
        {
            if(Cap[x][*itr] == 0)
                continue;

            int nod = *itr;
            int newCost = Cost[x][nod] - potential[*itr] + potential[x];
            int newD = dist[x] + newCost;
            if(dist[nod] > newD)
            {
                dist[nod] = newD;
                reald[nod] = reald[x] + Cost[x][nod];
                heap.push(make_pair(dist[nod], nod));
                prec[nod] = x;
            }

        }
    }

    if(potential[D] == INF)
        return false;

    int minFlow = INF;
    for(int i = D; i != S; i = prec[i])
    {
        minFlow = min(minFlow, Cap[prec[i]][i]);
    }

    for(int i = D; i != S; i= prec[i])
    {
        Cap[prec[i]][i] -= minFlow;
        Cap[i][prec[i]] += minFlow;
    }

    MinCost += minFlow * reald[D];
    potential = reald;
    return true;
}

int main()
{
#ifdef ONLINE_JUDGE
	ostream &fout = cout;
	istream &fin = cin;
#else
	fstream fin(infile.c_str(), ios::in);
	fstream fout(outfile.c_str(), ios::out);
#endif	

    fin >> N >> M >> S >> D;

    prec.resize(N + 1);
    potential.resize(N + 1);
    reald.resize(N + 1);
    dist.resize(N + 1);
    Cap.resize( N + 1, vector<int>(N + 1, 0));
    Cost.resize(N + 1, vector<int>(N + 1, 0));

    G.resize(N + 1);
    for(int i = 0; i < M; i++)
    {
        int x, y, c, z;
        fin >> x >> y >> c >> z;

        G[x].push_back(y);
        G[y].push_back(x);
        Cost[x][y] = z;
        Cost[y][x] = -z;
        Cap[x][y] = c;
    }


    bellman();

    while(dijkstra())
    {

    }

    fout << MinCost << "\n";
#ifdef ONLINE_JUDGE
#else
    fout.close();
	fin.close();
#endif
}