#include<fstream>
#include<vector>
#include<queue>
#include<cstring>
using namespace std;

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

const int nmax = 355, inf = 1000000000;

vector <int> g[nmax];
queue<int> q;
int n,m,s,d;
int viz[nmax],p[nmax],dist[nmax];
int c[nmax][nmax],f[nmax][nmax],cost[nmax][nmax];

int BellmanFord()
{
    int i;
    while (q.size()) q.pop();
    q.push(s);
    for (i=1;i<=n;i++) viz[i]=0;
    viz[s]=1;
    for (i=1;i<=n;i++) dist[i]=inf;
    dist[s]=0;
    while (!q.empty())
    {
        int v=q.front(); q.pop();
        if (v==d) continue;
        for (i=0;i<g[v].size();i++)
        {
            int to=g[v][i], len=cost[v][to];
            if (f[v][to]==c[v][to]) continue;
            if (dist[v]+len<dist[to])
            {
                dist[to]=dist[v]+len;
                p[to]=v;
                q.push(to);
            }
        }
    }
    if (dist[d]!=inf) return 1;
    return 0;
}


int main()
{
    cin>>n>>m>>s>>d;
    int i;
    for (i=1;i<=m;i++)
    {
        int x,y,z,t;
        cin>>x>>y>>z>>t;
        g[x].push_back(y);
        g[y].push_back(x);
        c[x][y]=z;
        cost[x][y]=t;
        cost[y][x]=-t;
    }

    int flow=0,mflow=0;
    while (BellmanFord())
    {
        int j;
        mflow=inf;
        for(j=d;j!=s;j=p[j])
            mflow=min(mflow,c[p[j]][j]-f[p[j]][j]);
        for (j=d;j!=s;j=p[j])
        {
            f[p[j]][j]+=mflow;
            f[j][p[j]]-=mflow;
        }
        flow+=dist[d]*mflow;
    }
    cout<<flow;
    return 0;
}