#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

#define FOR(i, a, b) for (int i=a; i<(b); i++)
#define F0R(i, a) for (int i=0; i<(a); i++)
#define FORd(i,a,b) for (int i = a; i >= b; i--)
#define F0Rd(i,a) for (int i = a; i >= 0; i--)
#define FORit(it,a) for (auto it = a.begin(); it != a.end(); it++)
#define trav(a,x) for (auto& a: x)

#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define ff first
#define ss second
#define all(x) x.begin(), x.end()
#define alla(arr, sz) arr, arr + sz

const int dx[4] = { 1,0,-1,0 }, dy[4] = { 0,1,0,-1 }; // for every grid problem!!
const ll linf = 4*1e18;
const int inf = 1000000007;

namespace io {
    void setIn(string s) { freopen(s.c_str(),"r",stdin); }
    void setOut(string s) { freopen(s.c_str(),"w",stdout); }
    void setIO(string s = "") {
        ios_base::sync_with_stdio(0); cin.tie(0); // fast I/O
        if (sz(s)) { setIn(s+".in"), setOut(s+".out"); } // for USACO
    }
}

using namespace io;

#define DEBUG 0

int start, finish; 
vector<vector<pii>> parent; 
vector<bool> visited; 
int sum_pave;

void dfs(int v) {
    if (v == start) return;
    visited[v] = 1; 
    trav(x,parent[v]) {
        sum_pave += x.ss;
        if (!visited[x.ff]) dfs(x.ff);
    }
}

void solve() {
    int n, m; cin >> n >> m >> start >> finish; start--; finish--; 
    vector<pii> adj[n];
    int sum_all_edges = 0; 

    F0R(i,m) {
        int a, b, c; cin>> a >> b >> c;
        a--; b--;
        sum_all_edges += c; 
        adj[a].pb(mp(b,c));
        adj[b].pb(mp(a,c));
    }
 
    parent.resize(n); 

    ll dist[n];
    dist[0] = 0; 
    FOR(i,1,n) dist[i] = linf;
 
    set<pll> s; // (cost, to)
    s.insert(mp(start,0));
    while (s.size() != 0) {
        pll p = *s.begin(); 
        s.erase(s.begin());
        ll v = p.ss, c = p.ff; 
 
        trav(x, adj[v]) {
            int to = x.ff, cost = x.ss; 
            ll new_price = c + cost; 
            if (new_price < dist[to]) { 
                s.erase(mp(dist[to], to)); 
                dist[to] = new_price; 
                s.insert(mp(dist[to], to));

                parent[to].clear(); 
                parent[to].pb(mp(v,cost));
            }
            else if (new_price == dist[to]) {
                parent[to].pb(mp(v,cost)); 
            }
        }
    }

    visited.assign(n,0);
    sum_pave = 0;
    dfs(finish);
    cout << sum_all_edges - sum_pave; 
}

int main() {
  #if DEBUG
  setIn("test.in");
  #else
  setIO();
  #endif

  int t;
  t= 1;  
  //cin >> t;
  while (t--) 
    solve();

  return 0;
}