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

int vector[100024];
int sir[100024];
int sate[100024];


int main()
{
	ifstream citire("sate.in");
	ofstream scriere("sate.out");
	int N,M,x,y,a,Suma;
	citire>>N>>M>>x>>y;
	int OK=Suma=0;
	int Max=0;
	int Min=0;
	for(a=0;a<M;a++)
	{
		citire>>vector[a]>>sir[a]>>sate[a];
		if(vector[a]==x)
		{
			Suma=0;
			Min=x;
			Suma+=sate[a];
			Max=sir[a];
		}
	}
	while(OK==0)
	{
		for(a=0;a<M;a++)
		{
			//if(Min!=x)
			//{
				/*if(vector[a]==x)
				{
					Min=x;
					Suma+=sate[a];
					Max=sir[a];
					break;
				}
			}
			else*/
			//{
				if(sir[a]==Max && vector[a]!=Min)
				{
					Suma-=sate[a];
					Max=vector[a];
				}
				else if(vector[a]==Max)
				{
					Suma+=sate[a];
				Max=sir[a];
				}
			//}
			if(Max==y)
			{
				OK=1;
				break;
			}
		}
	}
	scriere<<Suma;
}