#include <fstream>
#include <vector>
using namespace std;
ifstream fin("state.in");
ofstream fout("state.out");
struct idk
{
    int a,b;
};
idk aux;
vector <idk> v[30004];
int v1[30004];
int n,m,x,y,x1,y1,s;
int main()
{
    fin>>n>>m>>x>>y;
    for(int i=1;i<=m;i++)
    {
        fin>>x1>>y1>>s;
        aux.a=y1;
        aux.b=s;
        v[x1].push_back(aux);
        aux.a=x1;
        v[y1].push_back(aux);
    }
    for(int i=1;i<=n;i++)
    {
        for(int j=0;j<v[i].size();j++)
        {
            aux=v[i][j];
            if(v1[aux.a]>v1[i]+aux.b || v1[aux.a]==0)
            {
                v1[aux.a]=v1[i]+aux.b;
            }
        }
    }
    fout<<v1[y]-v1[x];
    return 0;
}