#include <cstdio>
#include <vector>
#include <queue>
using namespace std;
const int Max = 30007;
int n,m,vaz[Max],x,y;
long long d[Max];
vector<pair<int,long long> > drum[Max];
queue<int> q;
void bfs()
{
    vaz[x]=true;
    q.push(x);
    while(!q.empty())
    {
        x=q.front();
        q.pop();
        if(x==y)
        {
            break;
        }
        for(int i=0;i<drum[x].size();++i)
        {
            if(!vaz[drum[x][i].first])
            {
                vaz[drum[x][i].first]=true;
                d[drum[x][i].first]=d[x]+drum[x][i].second;
                q.push(drum[x][i].first);
            }
            else if(d[drum[x][i].first]>d[x]+drum[x][i].second)
            {
                vaz[drum[x][i].first]=true;
                d[drum[x][i].first]=d[x]+drum[x][i].second;
                q.push(drum[x][i].first);
            }
        }
    }
}

int main()
{
    int sat1,sat2,l;
    freopen("sate.in","r",stdin);
    freopen("sate.out","w",stdout);
    scanf("%d%d%d%d",&n,&m,&x,&y);
    if(x>y) swap(x,y);
    for(int i=1;i<=m;++i)
    {
        scanf("%d%d%d",&sat1,&sat2,&l);
        drum[sat1].push_back(make_pair(sat2, l));
        l*= -1;
        drum[sat2].push_back(make_pair(sat1, l));
    }
    bfs();
    printf("%lld",d[y]);
    return 0;
}