#include<cstdio>
#include<vector>
#include<cstring>
#include<queue>
#include<cmath>
#include<algorithm>
using namespace std;

FILE *fin = freopen("fmcm.in", "r", stdin);
FILE *fout = freopen("fmcm.out", "w", stdout);

const int MAX_N = 355;
const int INF = 2000000000;
int N, M, S, D;
int ans;
int dist[MAX_N], fromWhere[MAX_N], flow[MAX_N][MAX_N];
int cost[MAX_N][MAX_N], carry[MAX_N][MAX_N];
bool used[MAX_N];

vector < int > v[MAX_N];
queue < int > q;

int BellmanFord()
{
    for (int i = 1; i <= N; i++)
    dist[i] = INF,
    fromWhere[i] = -1;

    memset(used, 0, sizeof(used));
    dist[S] = 0;
    used[S]= 1;
    q.push(S);

    while (!q.empty())
    {
        int p = q.front();
        q.pop();

        vector < int > :: iterator it;
        for (it = v[p].begin(); it != v[p].end(); it++)
            if (carry[p][*it] - flow[p][*it] && dist[*it] > dist[p] + cost[p][*it])
            {
                dist[*it] = dist[p] + cost[p][*it];
                fromWhere[*it] = p;
                if (!used[*it])
                {
                    used[*it] = 1;
                    q.push(*it);
                }

            }
    }

    if (dist[D] != INF)
    {
        int cf = INF;
        for (int i = D; i != S; i = fromWhere[i])
            cf = min(cf, carry[fromWhere[i]][i] - flow[fromWhere[i]][i]);
        for (int i = D; i != S; i = fromWhere[i])
        {
            flow[fromWhere[i]][i] += cf;
            flow[i][fromWhere[i]] -= cf;
        }

        ans += cf * dist[D];
        return 1;
    }

    return 0;
}

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

    for (int i = 1, A, B, C, Z; i <= M; i ++)
    {
        scanf("%d%d%d%d", &A, &B, &C, &Z);
        v[A].push_back(B);
        v[B].push_back(A);

        cost[A][B] = Z;
        cost[B][A] = -Z;
        carry[A][B] = C;
    }

    while(BellmanFord());

    printf("%d\n", ans);
}