#include <cstdio>
#include <cstring>
#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
#include <stack>
#include <queue>
#include <list>
//#include <windows.h>
//#include <conio.h>
#include <cstdlib>
#include <time.h>
#include <limits.h>
#include <string>
#include <math.h>
using namespace std;
#define forA(V,it) for (typeof(V.begin()) it=V.begin();it!=V.end();it++)
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define ll long long
#define ull unsigned ll
#define MOD 1000000007
#define INF (1<<31)-1
#define MINF -(1<<31)
#define vi vector <int>
#define vll vector <ll>
#define pii pair <int,int>
#define pll pair <ll,ll>
#define newl printf("\n")
#define DIM 10000000
int N,M,nodS,nodF,i,x,y,c,cost[30005],used[30005];
vector < pii > G[30005];
queue < int > Q;
void BFS(int nod)
{
    used[nod]=true;
    Q.push(nod);
    for (int i=1;i<=N;i++) cost[i]=INF;
    cost[nod]=0;
    while (!Q.empty())
    {
        int x=Q.front();
        used[x]=true;
        if (x==nodF)
        {
            printf("%d",cost[nodF]);
            return;
        }
        for (vector< pii >::iterator it=G[x].begin();it!=G[x].end();it++)
        {
            if (!used[it->fi])
            {
                if (cost[x]+it->se<cost[it->fi]) cost[it->fi]=cost[x]+it->se;
                Q.push(it->fi);
            }
        }
        Q.pop();
    }
}
int main()
{
    freopen("sate.in","r",stdin);
    freopen("sate.out","w",stdout);
    scanf("%d %d %d %d",&N,&M,&nodS,&nodF);
    for (i=1;i<=M;i++)
    {
        scanf("%d %d %d",&x,&y,&c);
        G[x].pb(mp(y,c));
        G[y].pb(mp(x,-c));
    }
    BFS(nodS);
    //printf("%d",cost[nodF]);
    return 0;
}