#include<cstdio>
#include<vector>

#define NM 30002

using namespace std;

struct elem
{
    int d,to;
};

vector <elem> a[NM];

int n,st,end;
bool viz[NM];
int D[NM];

void read()
{
    int m;
    int x,y,dr;
    scanf("%d %d %d %d",&n,&m,&st,&end);

    while(m--)
        {
            scanf("%d %d %d",&x,&y,&dr);
            a[x].push_back((elem){dr,y});
            a[y].push_back((elem){-dr,x});
        }
}

void dfs(int pos)
{
    for(size_t i=0;i<a[pos].size();++i)
        if(!viz[a[pos][i].to])
        {
        viz[a[pos][i].to]=1;
        D[a[pos][i].to] = D[pos]+a[pos][i].d;
        dfs(a[pos][i].to);
        }
}

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

    read();

    viz[st]=1;
    dfs(st);
    printf("%d",D[end]);

    return 0;
}