#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

bool stop = false;
long dresult;
long long d[30001] = {0};
//vector< vector<short int> > val(30001, vector<short int>(30001));
short int val[30001][30001];
int n;

void get(int x, int dc, int v) {
	if(v==x) {dresult=dc;stop=true;}
	if(stop) return;
	while(d[x]!=0) {
		int y = d[x]%(n+1);
		int value = val[x][y];
		if(x>y) value *= -1;
		int dcp = dc;
		dcp += value;
		d[x] /= n+1;
		get(y, dcp, v);
	}
}

int main() {
	int m,x,y;
	ifstream fin("sate.in");
	ofstream fout("sate.out");
	fin>>n>>m>>x>>y;
	for(int i=1;i<=m;i++) {
		int x0,y0,d0;
		fin>>x0>>y0>>d0;
		val[x0][y0]=d0;
		d[x0]*=n+1;
		d[x0]+=y0;
		val[y0][x0]=d0;
		d[y0]*=n+1;
		d[y0]+=x0;
	}
	dresult=0;
	get(x,0,y);
	fout<<dresult;
	return 0;
}