#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\n”,Bellman-ford(a,b));

}

return 0;

}