#include <iostream>
#include <cstring>
#include <fstream>
#include <vector>
#include <queue>

#define N 30005

using namespace std;

ifstream fin("sate.in");
ofstream fout("sate.out");

vector <int> v[N], d[N], dis(N, 0);
vector <bool> viz(N, 0);
queue <short> q;
int num[6];

bool Nr(char x) { return (x >= '0' && x <= '9');}

int main()
{
    int n, m, x, y, k;
    fin>>n>>m>>x>>y; fin.get();
    char s[50];
    while(m--)
    {
        fin.getline(s, 50);
        k = 0;
        for(int i=0; s[i]; i++)
            if(Nr(s[i]))
            {
                k++;
                while(Nr(s[i]))
                    num[k] = num[k] * 10 + s[i] - '0', i++;
            }

        v[num[1]].push_back(num[2]);
        v[num[2]].push_back(num[1]);
        d[num[1]].push_back(num[3]);
        d[num[2]].push_back(-num[3]);

        for(int i=0; i<6; i++)
            num[i] = 0;
    }

    viz[x] = 1;

    q.push(x);
    while(!q.empty() && !viz[y])
    {
        int z = q.front();
        q.pop();
        for(unsigned i=0; i<v[z].size(); i++)
            if(!viz[v[z][i]])
            {
                viz[v[z][i]] = 1;
                dis[v[z][i]] = dis[z] + d[z][i];
                q.push(v[z][i]);
            }
    }

    fout<<dis[y];
    return 0;
}