#include <fstream>
#include <vector>
#include <queue>

#define  inf 1000000000

using namespace std;
ifstream fin("input.txt");
ofstream fout("output.txt");
int main()
{
    int N,M,da,to,a,b,p;
    da--;
    to--;
    fin>>N>>M;
    fin>>da>>to;
    vector<pair<int,int>> G[N];
    for(int i=0; i<M; i++)
    {
        fin>>a>>b>>p;
        a--;
        b--;
        G[a].push_back(make_pair(b,p));
        G[b].push_back(make_pair(a,p));
    }
    vector<int> dist(N,inf);
    queue<int> q;
    q.push(da);
    dist[da]=0;
    while(!q.empty())
    {
        int curr=q.front();
        q.pop();
        for(auto x:G[curr])
        {
            if(dist[curr]+x.second<dist[x.first])
            {
                q.push(x.first);
                dist[x.first]=dist[curr]+x.second;
            }
        }
    }
    fout<<dist[to];
}