#include <queue>
#include <stdio.h>
#include <vector>

const int MAX_N = 30000;
const int INF = 2e9;

struct Node {
  int u;
  int d;
};
std::vector<Node> G[1 + MAX_N];
int dist[1 + MAX_N];
bool inQ[1 + MAX_N];

int main() {

  freopen("sate.in", "r", stdin);
  freopen("sate.out", "w", stdout);

  int n, m, x, y;
  scanf("%d%d%d%d", &n, &m, &x, &y);
  for (int i = 1; i <= m; i++) {
    int u, v, d;
    scanf("%d%d%d", &u, &v, &d);
    G[u].push_back(Node{v, d});
    G[v].push_back(Node{u, -d});
  }
  for (int i = 1; i <= n; i++)
	dist[i] = INF;
  dist[x] = 0;
  std::queue<int> bfQ;
  bfQ.push(x);
  inQ[x] = true;
  while (!bfQ.empty() && !inQ[y]) {
    int u = bfQ.front();
    bfQ.pop();
    inQ[u] = false;
    for (Node e : G[u]) {
      if (dist[u] + e.d < dist[e.u]) {
        dist[e.u] = dist[u] + e.d;
        if (!inQ[e.u]) {
          bfQ.push(e.u);
          inQ[e.u] = true;
        }
      }
    }
  }

  printf("%d\n", dist[y]);

  fclose(stdin);
  fclose(stdout);

  return 0;
}