#include <algorithm>
#include <cstdio>
#include <cstring>
#include <vector>
#include <queue>
#define  MaxN 30005
#define INF 2140000000
#define MAX 131072
using namespace std;
  
FILE *IN,*OUT;
int pos=0,N,M,X,Y,Z,Alpha,Beta,Cost[MaxN],Nodes=0;
queue <int> Q;
vector <pair<int,int>> Graph[MaxN];
char f[MAX];
void Read(int &nr)
{
    nr=0;
    while(f[pos]>'9'||f[pos]<'0')
    {
        pos++;
        if(pos==MAX)
            pos=0,fread(f,1,MAX,IN);
    }
    while(f[pos]<='9'&&f[pos]>='0')
    {
        nr=nr*10+f[pos++]-'0';
        if(pos==MAX)
            pos=0,fread(f,1,MAX,IN);
    }
}
void BFS(int node,int *v)
{
    v[node]=0;
    Q.push(node);
    while(!Q.empty())
    {
        for(int i=0;i<Graph[Q.front()].size();i++)
            if(v[Graph[Q.front()][i].first]>v[Q.front()]+Graph[Q.front()][i].second)
                v[Graph[Q.front()][i].first]=v[Q.front()]+Graph[Q.front()][i].second,Q.push(Graph[Q.front()][i].first);
        Q.pop();
    }
}
int main()
{
    IN=fopen("sate.in","r");
    OUT=fopen("sate.out","w");
    fread(f,1,MAX,IN);
    Read(N),Read(M),Read(Alpha),Read(Beta);
    for(int i=1;i<=M;i++)
    {
        Read(X),Read(Y),Read(Z);
        Graph[X].push_back(make_pair(Y,Z));
        Graph[Y].push_back(make_pair(X,-Z));
    }
    for(int i=1;i<=N;i++)
        Cost[i]=INF;
    BFS(Alpha,Cost);
    fprintf(OUT,"%d",Cost[Beta]);
    return 0;
}