#include<cstdio>
#include<vector>

using namespace std;

const int N = 30005;
const int M = 100050;

int n, m, x, y, dist[N], xx[M];
vector< pair<int, int> > vecin[N];

void citire() {
	scanf("%d%d%d%d", &n, &m, &x, &y);
	
	for (int i = 1; i <= m; ++i) {
		int x1, y1, c;
		scanf("%d%d%d", &x1, &y1, &c);
		
		vecin[x1].push_back(make_pair(y1, c));
		vecin[y1].push_back(make_pair(x1, -c));
	}
}

inline void schimb(int &x, int &y) {
	int aux = x;
	x = y;
	y = aux;
}

void bfs() {
	xx[0] = x;
	
	int p = 0, q = 0;
	
	while (p <= q) {
		for (int i = 0; i < (int) vecin[xx[p]].size(); ++i) {
			int xc = vecin[xx[p]][i].first;
			
			if (xc != x && (dist[xc] == -1 || dist[xc] > dist[xx[p]] + vecin[xx[p]][i].second) ) {
				dist[xc] = dist[xx[p]] + vecin[xx[p]][i].second;
				
				xx[++q] = xc;
			}
			
			if (dist[y] != -1)
				return;
		}
		
		++p;
	}
}

int main() {
	freopen("sate.in", "r", stdin);
	freopen("sate.out", "w", stdout);
	
	citire();
	
	if (x > y)
		schimb(x, y);
	
	for (int i = 0; i < N; ++i)
		dist[i] = -1;
	
	dist[x] = 0;
	
	bfs();
	
	printf("%d\n", dist[y]);
	
	return 0;
}