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

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

    int i, x, y, z, cap;

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

    for (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;
    }

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

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

    return 0;
}