int dis[N],pre[N],head[N],visit[N],yong;
void init() {
memset(head,-1,sizeof(head));
yong=0;
}
void build(int u,int v,int w,int f) {
bian[yong].u=u;
bian[yong].v=v;
bian[yong].w=w;
bian[yong].f=f;
bian[yong].next=head[u];
head[u]=yong++;
}
void adde(int u,int v,int w,int f) {
build(u,v,w,f);
build(v,u,-w,0);
}
int spfa(int s,int t) {
memset(visit,0,sizeof(visit));
memset(pre,-1,sizeof(pre));
for(int i=0;i<=t;i++)//注意是从0开始而不是从s开始
dis[i]=inf;
queue<int>q;
visit[s]=1;//必须是s
q.push(s);
dis[s]=0;
while(!q.empty ()) {
int u=q.front ();
for(int index=head[u];index!=-1;index=bian[index].next) {
int v=bian[index].v;
if(bian[index].f&&dis[v]>dis[u]+bian[index].w) {
dis[v]=dis[u]+bian[index].w;
pre[v]=index;
if(!visit[v]) {
visit[v]=1;
q.push (v);
}
}
}
q.pop();
visit[u]=0;//是u
}
if(dis[t]==inf)
return -1;
return dis[t];
}
int min_cost(int s,int t) {
int sum=0,k,i;
while((k=spfa(s,t))!=-1){
int minn=inf;
i=pre[t];
while(i!=-1) {
if(minn>bian[i].f)
minn=bian[i].f;
i=pre[bian[i].u];
}
sum=sum+minn*k;
i=pre[t];
while(i!=-1){
bian[i].f-=minn;
bian[i^1].f+=minn;
i=pre[bian[i].u];
}
}
return sum;
}