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

# define x first
# define y second

const char *FIN = "fmcm.in", *FOU = "fmcm.out";
const short MAX = 355, oo = 0x3f3f;

vector < pair <short, short> > G[MAX];
short C[MAX][MAX], F[MAX][MAX], dp[MAX], T[MAX], viz[MAX];
short N, M, S, D;
int cm;

queue <short> Q ;

inline void getmin (short &a, short b) {
    a = a < b ? a : b;
}

inline short dijkstra (void) {
    memset (dp, oo, sizeof (dp));
    dp[S] = 0;
    for (Q.push (S); !Q.empty ();) {
        short X = Q.front(); viz[X] = 0; Q.pop ();
        for (vector < pair <short, short> > :: iterator it = G[X].begin (); it != G[X].end (); ++it)
            if (dp[X] + it -> y < dp[it -> x] && C[X][it -> x] != F[X][it -> x]) {
                dp[it -> x] = dp[X] + it -> y, T[it -> x] = X;
                if (viz[it -> x] == 0)
                    viz[it -> x] = 1, Q.push (it -> x);
            }
    }
    return dp[D] != oo;
}

int main (void) {
    freopen (FIN, "r", stdin);

    scanf ("%hd %hd %hd %hd", &N, &M, &S, &D);
    for (short i = 1, x, y, z, c; i <= M; ++i) {
        scanf ("%hd %hd %hd %hd", &x, &y, &c, &z), C[x][y] = c;
        G[x].push_back (make_pair (y, +z));
        G[y].push_back (make_pair (x, -z));
    }
    for (short fmin = 0; dijkstra (); cm += fmin * dp[D]) {
        fmin = oo;
        for (short i = D; i != S; i = T[i])
            getmin (fmin, C[T[i]][i] - F[T[i]][i]);
        if (fmin * dp[D] > 0) break;
        for (short i = D; i != S; i = T[i])
            F[T[i]][i] += fmin, F[i][T[i]] -= fmin;
    }
    fprintf (fopen (FOU, "w"), "%d", cm);
}