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

using namespace std;

#define Nmax 30100

vector<int> l[Nmax],c[Nmax];
queue<int> q;
char v[Nmax];

int ret[Nmax];

int main()
{
        freopen("sate.in","r",stdin);
        freopen("sate.out","w",stdout);

        int n,m,x,y,a,b,C;

#define Dim 10000

int poz = 0;

char buf[Dim];

//init
fread(buf,1,Dim,stdin);

#define cit(x)						\
{							\
	x = 0;						\
	while(buf[poz] < '0' || buf[poz] > '9')		\
		if(++poz == dim)			\
			fread(buf,1,Dim,stdin);		\
	while(buf[poz] >= '0' && buf[poz] <= '9')	\
	{						\
		x = x*10 + buf[poz] - '0';		\
    		    if(++poz == Dim)			\
			fread(buf,1,Dim,stdin);		\
	}						\
}	

#define cit2(c)						\
{							\
	while(buf[poz] < 'A' || buf[poz] > 'Z')		\
		if(++poz == Dim)			\
			fread(buf,1,Dim,stdin);		\
	c = buf[poz];					\
}


        //scanf("%d%d%d%d",&n,&m,&x,&y);
cit(n) cit(m) cit(x) cit(y)

        for (int i=1;i<=m;++i)
        {
//                scanf("%d%d%d",&a,&b,&C);
cit(a) cit(b) cit(C)
                l[a].push_back(b); c[a].push_back(C);
                l[b].push_back(a); c[b].push_back(-C);
        }

        if(x > y) x^=y^=x^=y;
        
	q.push(x);
	v[x] = 1;
	int nod;

	while(!q.empty())
	{
		nod = q.front(); q.pop();
		if(nod == y) break;
        	for (int i=0;i<l[nod].size();++i)
		if(v[l[nod][i]] == 0)
      		{
	    		ret[l[nod][i]] = ret[nod] + c[nod][i];
	    		v[l[nod][i]] = 1;
			q.push(l[nod][i]);
		}
	}
        
        printf("%d\n",ret[y]);

        return 0;
}