#include<cstdio>
#include<queue>
#include<vector>
#include<bitset>
using namespace std;
struct graf
{
    short l;
    int r;
};
vector<graf>v[30001];
queue<short>q;
int n,m,st,dr,x,y,c,i;
int d[30001];
bitset<30001>viz;
void bf(int nod)
{
    viz[nod]=1;
    q.push(nod);
    int e=0;
    while(!q.empty() && e==0)
    {
        int x=q.front();
        q.pop();
        vector<graf>::iterator it;
        for(it=v[x].begin();it!=v[x].end();++it)
        {
            graf X=*it;
            if (viz[X.l]==0)
            {
                d[X.l]=d[x]+X.r;
                if (X.l==dr) {printf("%d\n",d[X.l]);e=1;break;}
                q.push(X.l);
            }
        }
    }
}
int main()
{
    freopen("sate.in","r",stdin);
    freopen("sate.out","w",stdout);
    scanf("%d%d%d%d",&n,&m,&st,&dr);
    for (i=1;i<=m;++i)
    {
        scanf("%d%d%d",&x,&y,&c);
        graf X;X.l=y;X.r=c;
        v[x].push_back(X);
        X.l=x,X.r=-c;
        v[y].push_back(X);
    }
    bf(st);
    return 0;
}