#include<cstdio>
#include<bitset>
#include<vector>
#include<deque>
#define mp make_pair
#define pb push_back
using namespace std;
const int NMAX = 30005;
int n,m,start,finish,i,x,y,c,C[NMAX];
vector<pair<int,int> > a[NMAX];
bitset<NMAX> B;
deque<int> Q;
int main()
{
    freopen("sate.in","r",stdin);
    freopen("sate.out","w",stdout);
    scanf("%d%d%d%d",&n,&m,&start,&finish);
    for(;m;m--)
    {
        scanf("%d%d%d",&x,&y,&c);
        a[x].pb(mp(y,c));
        a[y].pb(mp(x,-c));
    }
    for(i=1;i<=n;i++) C[i]=1<<30;
    Q.push_back(start); C[start]=0; B[start]=1;
    while(!Q.empty())
    {
        x=Q.front(); B[x]=1;
        for(i=0;i<a[x].size();i++)
        {
            y=a[x][i].first; c=a[x][i].second;
            if(C[x]+c<C[y])
            {
                C[y]=C[x]+c;
                if(!B[y]) {B[y]=1; Q.push_back(y);}
            }
        }
        Q.pop_front(); B[x]=0;
    }
    printf("%d\n",C[finish]);
    return 0;
}