#include <cstdio>
#include <vector>
#include <algorithm>
#include <climits>

#define INFILE "sate.in"
#define OUTFILE "sate.out"
#define NMax 32768

using namespace std;

int N, X, Y;
int Distance[NMax];
bool Visited[NMax];
vector<int> Links[NMax], Distances[NMax];

void go(int n)
{
	int m;

	for (int i = 0; i < Links[n].size() && !Visited[Y]; ++i)
	{
		m = Links[n][i];

		if (!Visited[m])
		{
			Distance[m] = Distances[n][i] + Distance[n];
			Visited[m] = true;
			go(m);
		}
	}
}

int main()
{
	int x, y, d, M;

	freopen(INFILE, "r", stdin);
	freopen(OUTFILE, "w", stdout);

	scanf("%d%d%d%d", &N, &M, &X, &Y);

	for (x = 1; x <= N; ++x)
	{
		Distance[x] = INT_MAX;
	}

	while (M--)
	{
		scanf("%d%d%d", &x, &y, &d);
		Links[x].push_back(y);
		Links[y].push_back(x);
		Distances[x].push_back(0 + d);
		Distances[y].push_back(0 - d);
	}

	Distance[X] = 0;
	go(X);

	printf("%d\n", Distance[Y]);

	return 0;
}