#include<cstdio>
int n,m,k,j,i,l,s,d,t,w,c[351][351],p[351],h[351],r[351],g[351][351],a[351],o[351][351],b[351],e;
int main()
{freopen("fmcm.in","r",stdin);
freopen("fmcm.out","w",stdout);
scanf("%d%d%d%d",&n,&m,&s,&d);
while(m--)
          scanf("%d%d%d%d",&i,&j,&o[i][j],&c[i][j]),g[i][a[i]++]=j,g[j][a[j]++]=i,o[j][i]=-o[i][j];
while(1)      
          {for(i=1;i<=n;i++)
                   b[i]=10001,h[i]=r[i]=i;
          b[s]=p[d]=0,h[1]=r[1]=s,l=n,h[s]=r[s]=1;
          while(l>1&&!p[d])
                   {for(k=0;k<a[h[1]];k++)
                          {j=g[h[1]][k];
                          if(b[j]>b[h[1]]+o[h[1]][j]&&c[h[1]][j])
                                 {b[j]=b[h[1]]+o[h[1]][j],p[j]=h[1];
                                 for(t=r[j];t>3&&b[h[t]]<b[h[t/2]];t/=2)
                                       w=h[t],h[t]=h[t/2],h[t/2]=w,r[h[t]]=t,r[h[t/2]]=t/2;}}
                   h[1]=h[l--],r[h[1]]=1;
                   if(l>1)
                          for(j=1,t=0;j!=t;)
                                 {t=j;
                                 if(2*t<=l&&b[h[j]]>b[h[2*t]])
                                       j=2*t;
                                 if(2*t<l&&b[h[j]]>b[h[2*t+1]])
                                       j=2*t+1;
                                 k=h[j],h[j]=h[t],h[t]=k,r[h[j]]=j,r[h[t]]=t;}}
          if(!p[d])
                   break;
          for(m=10001,l=d;l!=s;l=p[l])
          if(m>c[p[l]][l])
                   m=c[p[l]][l];
          for(l=d;l!=s;l=p[l])
                   c[p[l]][l]-=m,c[l][p[l]]+=m;
          e=e+b[d]*m;}
printf("%d",e);
return 0;}