#include <algorithm>
#include <vector>
using namespace std;

#define DIM ( 1<<9 )
#define INF ( 1<<30 )
#define pb push_back
#define sz size()

int n, m, rez, cd[ DIM*DIM ], tat[ DIM ], val[ DIM ], viz[ DIM ], cst[ DIM ][ DIM ], flx[ DIM ][ DIM ];
int S, D;
vector< int > vec[ DIM ];

void init_val() {

    int i;

    for( i = 1; i <= n; ++i )
        val[ i ] = INF;
}

void init_viz() {

    int i;

    for( i = 1; i <= n; ++i )
        viz[ i ] = 0;
}

int bellman_ford() {

    int st, dr, aux, nod;
    unsigned int i;

    init_val();
    init_viz();
    cd[ 0 ] = S;
    viz[ S ] = 1;
    for( st = dr = 0; st <= dr; ++st ) {

        nod = cd[ st ];
        viz[ nod ] = 0;
        for( i = 0; i < vec[ nod ].sz; ++i ) {

            aux = vec[ nod ][ i ];
            if( val[ nod ] + cst[ nod ][ aux ] < val[ aux ] && flx[ nod ][ aux ] > 0 ) {

                if( !viz[ aux ] ) {

                    viz[ aux ] = 1;
                    cd[ ++dr ] = aux;
                }
                val[ aux ] = val[ nod ] + cst[ nod ][ aux ];
                tat[ aux ] = nod;
            }
        }
    }
    return val[ D ] != INF;
}

void read() {

    int i, x0, y0, cst0, flx0;

    scanf( "%d %d %d %d", &n, &m, &S, &D );
    for( i = 1; i <= m; ++i ) {

        scanf( "%d %d %d %d", &x0, &y0, &flx0, &cst0 );
        cst[ x0 ][ y0 ] = cst0;
        flx[ x0 ][ y0 ] = flx0;
        vec[ x0 ].pb( y0 );
    }
}

void solve() {

    int nod, fmin;

    while( bellman_ford() ) {

        fmin = INF;
        for( nod = D; nod != S; nod = tat[ nod ] )
            fmin = min( fmin, flx[ tat[ nod ] ][ nod ] );
        for( nod = D; nod != S; nod = tat[ nod ] ) {

            flx[ tat[ nod ] ][ nod ] -= fmin;
            flx[ nod ][ tat[ nod ] ] += fmin;
        }
        rez += fmin*val[ D ];
    }
    printf( "%d", rez );
}

int main() {

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

    read();
    solve();

    return 0;
}