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| #include<cstdio>
#include<queue>
#include<cstring>
using namespace std;
const int N=125100;
int n,m,s,t,tot=1,hd[(int)6e4],cur[(int)6e4],ss,tt,dep[(int)6e4];
long long flow[(int)6e4],l[N];
struct Edge
{
int to,nxt;
long long val;
}e[N*3+99];
inline void add(int u,int v,long long w){
e[++tot]={v,hd[u],w},hd[u]=tot;
e[++tot]={u,hd[v],0ll},hd[v]=tot;
}
bool bfs(int st,int en){
for(int i=0;i<=n+2;++i)dep[i]=0;
queue<int> q;
memcpy(cur,hd,sizeof(hd));
q.push(st);
dep[st]=1;
while(!q.empty()){
int u=q.front();
q.pop();
for(int eg=hd[u];eg;eg=e[eg].nxt){
if(!dep[e[eg].to]&&e[eg].val>0){
dep[e[eg].to]=dep[u]+1;
q.push(e[eg].to);
}
}
}
return !!dep[en];
}
long long dfs(int u,int en,long long flow){
if(u==en)return flow;
long long r=flow;
for (int eg = cur[u]; eg && r; eg = e[eg].nxt)
{
cur[u] = eg;
if (e[eg].val>0 && dep[e[eg].to] == dep[u] + 1)
{
long long c = dfs(e[eg].to,en, min(r, e[eg].val));
r -= c;
e[eg].val -= c;
e[eg ^ 1].val += c;
}
}
return flow - r;
}
long long Dinic(int st,int en){
long long ret=0;
while(bfs(st,en))ret+=dfs(st,en,1ll<<53);
return ret;
}
int main(){
long long tmp,sum=0;
scanf("%d%d%d%d",&n,&m,&s,&t);
tt=n+1;
for(int i=1,w,x;i<=m;++i){
long long y,z;
scanf("%d%d%lld%lld",&w,&x,&y,&z);
l[i]=y;
add(w,x,z-y);
flow[w]-=l[i],flow[x]+=l[i];
}
for(int i=1;i<=n;++i){
if(flow[i]>0){
sum+=flow[i];
add(ss,i,flow[i]);
}else if(flow[i]<0)add(i,tt,-flow[i]);
}
add(t,s,1ll<<53);
if(sum==Dinic(ss,tt)){
tmp=e[tot].val;
e[tot].val=e[tot^1].val=0;
printf("%lld\n",tmp - Dinic(t, s));
}else puts("please go home to sleep");
return 0;
}
|