#include <iostream>
#include <fstream>
#include <queue>
#include <cstring>
#include <vector>
#define inf (1<<28)
#define node second
#define value first
#define nmax 30005
using namespace std;

FILE *fin=fopen ("sate.in","r");
FILE *fout=fopen ("sate.out","w");

vector <pair<int, int> > v[nmax];
queue <int> q;

int n, m, x, y;
int best[nmax];

void DRACU_STIE(int x){
    for(int i=1; i<=n; i++) best[i]= inf;
    best[x]= 0;
    q.push(x);
    while(!q.empty() || best[y] == inf){
        int cur= q.front();
        q.pop();
        for(int i=0; i<v[cur].size(); i++){
            if(best[v[cur][i].node] > best[cur]+v[cur][i].value){
                best[v[cur][i].node]= best[cur]+v[cur][i].value;
                q.push(v[cur][i].node);
            }
        }
    }
}

int main(){
    int a, b, c;
    fscanf(fin, "%d%d%d%d", &n, &m, &x, &y);
    for(int i=1; i<=m; i++){
        fscanf (fin ,"%d%d%d",&a, &b, &c);
        v[a].push_back(make_pair(c, b));
        v[b].push_back(make_pair(-c, a));
    }
    DRACU_STIE(x);
    fprintf(fout,"%d", best[y]);
    return 0;
}