#include<stdio.h>
#include<algorithm>
#include<iostream>
#include<queue>
using namespace std;
#define N 2100
struct node {
int u,v,w,next;
}bian[N];
int n,m,yong,head[N];
void creat(int u,int v,int w) {
bian[yong].u=u;
bian[yong].v=v;
bian[yong].w=w;
bian[yong].next=head[u];
head[u]=yong++;
}
void Dcreat(int u,int v,int w) {
creat(u,v,w);
creat(v,u,w);
}
int Bellman-ford(int u,int s) {
int cur,dis[N],i,visit[N],v;
queue<int>q;
memset(visit,0,sizeof(visit));
for(i=0;i<n;i++)
dis[i]=1000000000;
dis[u]=0;
q.push(u);
visit[u]=1;
while(!q.empty()) {
u=q.front();
q.pop();
visit[u]=0;
for(i=head[u];i!=-1;i=bian[i].next) {
v=bian[i].v;
if(dis[v]>bian[i].w+dis[u]) {
dis[v]=bian[i].w+dis[u];
if(!visit[v]) {
visit[v]=1;
q.push(v);
}
}
}
}
for(i=0;i<yong;i++)//判断是否存在负权路
if(dis[bian[i].v]>dis[bian[i].u]+bian[i].w)//
return -1;
if(dis[s]<1000000000)
return dis[s];
return -1;
}
int main() {
int a,b,k;
while(scanf("%d%d",&n,&m)!=EOF) {
yong=0;
memset(head,-1,sizeof(head));
while(m--) {
scanf("%d%d%d",&a,&b,&k);
Dcreat(a,b,k);
}
scanf("%d%d",&a,&b);
printf("%d
",Bellman-ford(a,b));
}
return 0;
}