//fmcm
#include<bits/stdc++.h>
#define mp make_pair
#define N 510
#define Dim 2000000000
using namespace std;
vector <int> G[N];
queue <int> q;
	
int Cost[N][N],C[N][N],dist[N],dp[N],newdist[N],pred[N],f[N][N],viz[N];
int n,m,s,d;
	
class InParser {
private:
	FILE *fin;
	char *buff;
	int sp;
	
	char read_ch() {
		++sp;
		if (sp == 4096) {
			sp = 0;
			fread(buff, 1, 4096, fin);
		}
		return buff[sp];
	}
public:
	InParser(const char* nume) {
		fin = fopen(nume, "r");
		buff = new char[4096]();
		sp = 4095;
	}
	InParser& operator >> (int &n) {
		char c;
		while (!isdigit(c = read_ch()) && c != '-');
		int sgn = 1;
		if (c == '-') {
			n = 0;
			sgn = -1;
		} else {
			n = c - '0';
		}
		while (isdigit(c = read_ch())) {
			n = 10 * n + c - '0';
		}
		n *= sgn;
		return *this;
	}
};

void read()
{
    InParser fin("fmcm.in");
    int i,x,y,z,cost;
    fin>>n>>m>>s>>d;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y>>z>>cost;
        G[x].push_back(y);
        G[y].push_back(x);
        Cost[x][y]=cost;
        Cost[y][x]=-cost;
        C[x][y]=z; //capacitatea
    }
}
	
bool still;
priority_queue<pair<int, int>, vector<pair<int, int> >, greater<pair<int, int> > > pq;

inline bool b_ford()
{
    int i,j,nod;
    for(i = 1; i <= n; ++i)
        dist[i] = Dim;
    dist[s] = 0;
    memset(viz,0,sizeof(viz));
    q.push(s);
    viz[s] = 1;
    while(!q.empty())
    {
        nod=q.front();
        q.pop();
	
        for(j=0;j<G[nod].size();j++) 
        if(C[nod][G[nod][j]] && dist[nod]+Cost[nod][G[nod][j]]<dist[G[nod][j]])
        {
            dist[G[nod][j]]=dist[nod]+Cost[nod][G[nod][j]];
            if(!viz[G[nod][j]])
            {
                q.push(G[nod][j]);
                viz[G[nod][j]]=1;
            }
        }
        viz[nod]=0;
    }
    return (dist[d] != Dim);
}
	
int Edmonds_Karp()
{
    int i;
    for(i = 1; i <= n; ++i){
        pred[i] = -1;
        dp[i] = Dim;
        viz[i] = 0;
    }
    dp[s] = 0;
    newdist[s] = 0;
    pq.push(mp(0,s));

    while(!pq.empty())
    {
        auto nod = pq.top();
        pq.pop();

        if(viz[nod.second])
            continue;
        viz[nod.second] = 1;
	
        for(auto& it: G[nod.second])
        if(!viz[it])
        if(C[nod.second][it] > f[nod.second][it])
        {
            int distance = nod.first + Cost[nod.second][it] + dist[nod.second] - dist[it];
            if(distance < dp[it]){
                //cerr<<it<<' '<<distance<<'\n';
                dp[it] = distance;
                pred[it] = nod.second;
                newdist[it] = newdist[nod.second] + Cost[nod.second][it];
                //if(!viz[it])
                    pq.push(mp(distance,it));
            }
        }
    }

    //cerr<<newdist[d]<<' '<<dp[d]<<'\n';
    //memcpy(dist,newdist,sizeof(dist));
    for(int i=1;i<=n;++i)
        dist[i] = newdist[i];

    if(dp[d] != Dim)
    {
        //cout<<dist[d]<<endl;
        still = 1;
        int aleg = Dim;
        for(i = d; i != s; i = pred[i])
            aleg = min(aleg, C[pred[i]][i] - f[pred[i]][i]);
        for(i = d; i != s; i = pred[i])
        {
            f[pred[i]][i] += aleg;
            f[i][pred[i]] -= aleg;
        }
        return aleg * newdist[d];
    }
    return 0;
}
	
 
long long answer()
{
    long long R = 0;
    still = 1;
    b_ford();
    while(still)
    {
        still = 0;
        R += Edmonds_Karp()*1ll;
        //cout<<R<<endl;
    }
    return R;
}
	
 
int main()
{
    read();
    freopen("fmcm.out","w",stdout);
    cout<<answer();
}