#include "bits/stdc++.h"

using namespace std;

void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifndef ONLINE_JUDGE
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif

using ll = long long;
using ull = unsigned long long;

const char nl = '\n';

int bfs(int root, int reach, vector<vector<pair<int, int>>> &adj) {
    int n = adj.size();
    vector<bool> been(n);
    vector<int> dist(n);
    queue<int> Q;
    Q.push(root);
    been[root] = true;

    while (!Q.empty()) {
        int nod = Q.front();
        Q.pop();
        for (auto u : adj[nod]) {
            if (been[u.second]) continue;
            been[u.second] = true;
            dist[u.second] = dist[nod] + u.first;
            Q.push(u.second);
        }
    }
    return dist[reach];
}

int32_t main() {
    freopen("sate.in", "r", stdin);
    freopen("sate.out", "w", stdout);
    ios::sync_with_stdio(false);
    cin.tie(0);

    int N, M, x, y;
    cin >> N >> M >> x >> y;

    vector<vector<pair<int, int>>> adj(N + 1);
    for (int i = 0; i < M; ++i) {
        int a, b, d;
        cin >> a >> b >> d;
        adj[a].push_back({d, b});
        adj[b].push_back({-d, a});
    }
    cout << bfs(x, y, adj) << nl;
    return 0;
}