#include<cstdio>
#include<vector>
#include<queue>

using namespace std;

#define Nmax 100025

int cost[Nmax], N, M, X, Y;
vector<pair<int, int> > G[Nmax];

void cod(int start) {
	queue<int> Q;
	int dist, nod, x;
	
	Q.push(start); 
	while(!Q.empty()) {
		x=Q.front();
		for(vector<pair<int, int> >:: iterator it=G[x].begin(), it2=G[x].end(); it!=it2; ++it) {
			nod=it->first; dist=it->second;
			if(!cost[nod]) {
				cost[nod]=cost[x]+dist;
				if(nod==Y)
					return;
				Q.push(nod);
			}
		}
		Q.pop();
	}
}

int main() {
	freopen("sate.in","r",stdin);
	freopen("sate.out","w",stdout);
	
	int x, y, c;
	
	scanf("%d %d %d %d",&N,&M,&X,&Y);
	while(M--) {
		scanf("%d %d %d",&x,&y,&c);
		G[x].push_back(make_pair(y,c));
		G[y].push_back(make_pair(x,-c));
	}
	cod(X);
	printf("%d\n",cost[Y]);
	
	return 0;
}