using namespace std;
#include <fstream>
#include <vector>
#include <queue>
ifstream fin("sate.in");
ofstream fout("sate.out");
const int Nmax = 30000;

int d[Nmax+1];
vector< pair<int, int> > v[Nmax+1];
queue<int> Q;

int mod(int a) {return a > 0 ? a : (-a);}

int main()
{
    int i, m, n, a, b, c, x, y, nod;
    vector< pair<int, int> >::iterator it;
    fin >> n >> m >> x >> y;
    for(; m; --m)
    {
        fin >> a >> b >> c;
        v[a].push_back(make_pair(b, c));
        v[b].push_back(make_pair(a, c));
    }
    d[x] = 0;
    for(Q.push(x); !Q.empty(); Q.pop())
    {
        nod = Q.front();
        for(it = v[nod].begin(); it != v[nod].end(); ++it)
            if((it->first) != x && d[it->first] == 0)
            {
                if(nod < it->first) d[it->first] = d[nod] + (it->second);
                else d[it->first] = d[nod] - (it->second);
                Q.push(it->first);
                if((it->first) == y) {fout << mod(d[y]) << '\n'; return 0;}
            }
    }
    return 0;
}