ac代码：
#include<iostream>
#include<cstring>
#include<queue>
using namespace std;
const int N=1010;
const int M=20020;
struct node{
int d,end,d1;
bool operator <(const node &x)const{
return d>x.d;
}
};
priority_queue<node>pq;
int dis[N],vis[N],h1[M],h2[M],ne[M],v[M],w[M],cnt[N];
int n,m,s,t,k,idx;
int ct=0;
void add(int h[],int ui,int vi,int wi){
ne[++idx]=h[ui]; h[ui]=idx;
v[idx]=vi;w[idx]=wi;
}
void dij(){
pq.push({0,t});
while(pq.size()){
node tmp=pq.top(); pq.pop();
if(vis[tmp.end]) continue;
vis[tmp.end]=1; dis[tmp.end]=tmp.d;
for(int i=h2[tmp.end];i;i=ne[i]){
if(vis[v[i]]) continue;
pq.push({tmp.d+w[i],v[i]});
}
}
}
int A(){
pq.push({dis[s],s,0});
while(pq.size()){
node tmp=pq.top(); pq.pop();
cnt[tmp.end]++;
if(tmp.end==t){ ct++; if(ct==k) return tmp.d;}
if(cnt[tmp.end]>k) continue;
for(int i=h1[tmp.end];i;i=ne[i]){
pq.push({tmp.d1+w[i]+dis[v[i]],v[i],tmp.d1+w[i]});
}
}
return -1;
}
int main(){
scanf("%d%d",&n,&m);
while(m--){
int ui,vi,wi;
scanf("%d%d%d",&ui,&vi,&wi);
add(h1,ui,vi,wi);
add(h2,vi,ui,wi);
}
scanf("%d%d%d",&s,&t,&k);
if(s==t) k++;
dij();
printf("%d",A());
return 0;
}