#include <stdio.h>
#include <vector>
#include <cstring>
#include <fstream>
using namespace std;

ifstream fin("fmcm.in");
ofstream fout("fmcm.out");

#define MaxN 510
#define inf 2000000000
#define ll long long
#define maxx 1000010


int N, M, S, D;
int Drum, L;
vector <int> A[MaxN];
int G[MaxN], Dist[MaxN], From[MaxN];
int Q[maxx], U[MaxN];
int C[MaxN][MaxN], F[MaxN][MaxN], Cost[MaxN][MaxN];

int BellmanFord()
{
    int i, j;

    for (i = 1; i <= N; i++)
    {

        Dist[i] = inf;
        From[i] = -1;
    }

    Dist[S] = 0;
    L = 1;
    Q[L] = S;
    memset(U, 0, sizeof(U));
    U[S] = 1;

    for (i = 1; i <= L; i++)
    {
        for (j=0; j<G[Q[i]]; j++)
            if (C[Q[i]][A[Q[i]][j]]-F[Q[i]][A[Q[i]][j]]>0 && Dist[Q[i]]+Cost[Q[i]][A[Q[i]][j]]<Dist[A[Q[i]][j]])
            {
                Dist[A[Q[i]][j]] = Dist[Q[i]] + Cost[Q[i]][A[Q[i]][j]];
                From[A[Q[i]][j]] = Q[i];
                if (!U[A[Q[i]][j]])
                {
                    Q[++L] = A[Q[i]][j];
                    U[Q[L]] = 1;
                }
            }

        U[Q[i]] = 0;
    }

    if (Dist[D] != inf)
    {
        int Vmin = inf;
        Drum = 1;

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

        for (i = D; i != S; i = From[i])
        {
            F[From[i]][i] += Vmin;
            F[i][From[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()
{
    int i, x, y, z, cap;

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

    for (i = 1; i <= M; i++)
    {
        fin >> 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;
    }

    for (i = 1; i <= N; i++) G[i] = A[i].size();

    fout <<  Flux();
    fin.close();
    fout.close();
    return 0;
}