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

using namespace std;

int n,m,x,y,s,d,c;
int cs[30001];
bool viz[30001];
queue<int> q;

struct sat
{
    vector<int> vecini;
    vector<int> cost;
} a[30001];

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

    scanf("%d %d %d %d",&n,&m,&x,&y);
    if(x>y)
    {
        int t=y;
        y=x;
        x=t;
    }

    for(int i=1;i<=m;i++)
    {
        scanf("%d %d %d",&s,&d,&c);
        if(s>d)
        {
            int t=d;
            d=s;
            s=t;
        }
        a[s].vecini.push_back(d);
        a[s].cost.push_back(c);
        a[d].vecini.push_back(s);
        a[d].cost.push_back(-c);
    }

    q.push(x);
    int current;
    while(!q.empty())
    {
        current=q.front();
        q.pop();
        if(current==y)
        {
            break;
        }
        int vc;
        int dst;
        while(!a[current].vecini.empty())
        {
            vc=a[current].vecini.back();
            dst=a[current].cost.back();
            if(viz[vc]==0)
            {
                viz[vc]=1;
                cs[vc]=cs[current]+dst;
                q.push(vc);
            }
            a[current].vecini.pop_back();
            a[current].cost.pop_back();
        }
    }
    printf("%d",cs[y]);
}