```cpp
#include<bits/stdc++.h>
#define int long long
using namespace std;
const int inf=1e18;
int n,m,s,t,ans,delta,w[205][205],f[205][205],pre[205];
bool vis[205];
struct edge{
int to,val;
};
vector<edge> G[205];
struct node{
int u,del;
};
void update(int u){
G[pre[u]][f[u][pre[u]]].val-=delta;
cout<<u<<' '<<pre[u]<<endl;
if(pre[u]!=s)
update(pre[u]);
}
queue<node> q;
inline bool EK(){
memset(vis,0,sizeof(vis));
while(q.size())
q.pop();
q.push(node({s,inf}));
while(q.size()){
int u=q.front().u,val=q.front().del;
q.pop();
for(auto N:G[u]){
int v=N.to,w=N.val;
if(!w)
continue;
if(vis[v])
continue;
vis[v]=1;
pre[v]=u;
if(v==t){
delta=min(val,w);
return 1;
}
q.push(node({v,min(val,w)}));
}
}
return 0;
}
signed main(){
scanf("%lld%lld%lld%lld",&n,&m,&s,&t);
for(int i=1,u,v,val;i<=m;++i){
scanf("%lld%lld%lld",&u,&v,&val);
w[u][v]+=val;
}
for(int i=1;i<=n;++i)
for(int j=1;j<=n;++j)
if(w[i][j])
f[j][i]=G[i].size(),G[i].push_back(edge({j,w[i][j]}));
while(EK())
update(t),ans+=delta;
printf("%lld\n",ans);
return 0;
}
```
by qwq___qaq @ 2023-05-12 00:13:51