#include <cstdio>
#include <iostream>
#include <vector>
#include <queue>

using namespace std;

vector<int> graf[360];
int n, m, s, d, cost[360][360], cap[360][360], f[360][360], dist[360], prev[360];
bool viz[360], drum;

const int INF = 0x3f3f3f3f;

long long BellmanFord()
{
     int i, j, x, vmin;
     deque<int> q;
     
     for(i = 1; i <= n; ++i)
     {
         viz[i] = false;
         dist[i] = INF;
     }
     viz[s] = true;
     dist[s] = 0;
     for(q.push_back(s); !q.empty(); q.pop_front())
     {
        int src = q.front();
        for(i = 0; i < graf[src].size(); ++i)
        {
             x = graf[src][i];
             if(cap[src][x] > f[src][x] && dist[x] > dist[src] + cost[src][x])
             {
                dist[x] = dist[src] + cost[src][x],
                prev[x] = src;
                if(!viz[x])
                {
                    q.push_back(x);
                    viz[x] = true;
                }
             }
        }
     }
     
     if(!viz[d]) return 0;
     
     drum = true;
     
     for(vmin = INF, i = d; i != s; i = prev[i]) vmin = min(vmin, cap[prev[i]][i] - f[prev[i]][i]);
     for(i = d; i != s; i = prev[i])
     {
         f[prev[i]][i] += vmin;
         f[i][prev[i]] -= vmin;
     };
     return vmin * dist[d];
}

long long flux()
{
    long long rez = 0;
    drum = true;
    while(drum)
    {
        drum = false;
        rez += BellmanFord();
    }
    return rez;
}

int main()
{
    int i, x, y, cp, cst;
    
    freopen("fmcm.in", "r", stdin);
    freopen("fmcm.out", "w", stdout);
    
    scanf("%d %d %d %d", &n, &m, &s, &d);
    for(i = 0; i < m; ++i) 
    {
        scanf("%d %d %d %d", &x, &y, &cp, &cst);
        graf[x].push_back(y);
        graf[y].push_back(x);        
        
        cost[x][y] = cst; 
        cost[y][x] = -cst;
        cap[x][y] = cp;
    }
    
    cout << flux() << "\n";

    return 0;
}