#include <fstream>
#include <vector>
#include <bitset>
#include <queue>
#include <algorithm>
#include <utility>
#include <string.h>

using namespace std;

ifstream cin("fmcm.in");
ofstream cout("fmcm.out");

const int MAXN = 355;
const int oo = (1<<31)-1;

typedef vector<int> Graph[MAXN];
typedef vector<int> :: iterator It;

Graph G;
int N, M, S, D, Capacity[MAXN][MAXN], Cost[MAXN][MAXN], Answer;
vector<int> Distance(MAXN, oo), Flow(MAXN), Father(MAXN);
priority_queue <pair<int, int> > Heap;
queue <int> Q;

inline bool BellmanFord(){
    for(Q.push(S), Distance[S] = 0 ; !Q.empty() ; Q.pop() ){
        int Node = Q.front();
        for(It it=G[Node].begin(), fin=G[Node].end(); it!=fin; ++it)
            if(Capacity[Node][*it] && Distance[*it] > Distance[Node] + Capacity[Node][*it]){
                Distance[*it] = Distance[Node] + Capacity[Node][*it];
                Q.push(*it);
            }
    }
}

inline bool Update_Flow(){
    fill(Distance.begin(), Distance.end(), oo);
    for(Distance[S] = 0, Heap.push(make_pair(0, S)), Flow[S] = 0 ; !Heap.empty() ; Heap.pop()){
        int Node = Heap.top().second;
        int d = -Heap.top().first;
        if(Distance[Node] < d)  continue;
        for(It it = G[Node].begin(), fin = G[Node].end() ; it != fin ; ++it)
            if( Capacity[Node][*it] ){
                d = Distance[Node] + Cost[Node][*it] - Distance[*it];
                if(Distance[*it] <= Distance[Node] + d) continue;
                Distance[*it] = Distance[Node] + d;
                Flow[*it] = Flow[Node] + Cost[Node][*it];
                Father[*it] = Node;
                Heap.push(make_pair(-Distance[*it], *it));
            }
    }
    Flow = Distance;
    return Distance[D] != oo;
}

int main()
{
    cin >> N >> M >> S >> D;
    for(int i = 1 ; i <= M ; ++ i){
        int x, y, z, c;
        cin >> x >> y >> c >> z;
        G[x].push_back(y);
        G[y].push_back(x);
        Capacity[x][y] = c;
        Cost[x][y] = z;
        Cost[y][x] = -z;
    }
    //BellmanFord();
    for(int flow ; Update_Flow() ; Answer += flow*Flow[D] ){
        flow = oo;
        for(int i = D ; i != S ; i = Father[i])
            flow = min (flow, Capacity[Father[i]][i]);
        for(int i = D ; i != S ; i = Father[i])
            Capacity[Father[i]][i] -= flow,
            Capacity[i][Father[i]] += flow;
    }
    cout << Answer << "\n";
    cin.close();
    cout.close();
    return 0;
}