#include<bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define ll long long

int main()
{
    ll n,m,p,q,k,hell=1e12;
    cin>>n>>m>>p>>q>>k;
    vector<pair<ll,ll> > adj[n+1];
    vector<vector<bool> >vis(n+1,vector<bool>(k+1,0));
    vector<vector<ll> >dis(n+1,vector<ll>(k+1,hell));
    for(int i=0;i<m;i++)
    {
        ll x,y,z;
        cin>>x>>y>>z;
        adj[x].push_back({y,z});
        adj[y].push_back({x,z});
    }
    for(int i=0;i<=k;i++) dis[p][i]=0;
    priority_queue<tuple<ll,ll,ll> >pq;
    pq.push({0,p,0});
    while(!pq.empty())
    {
        ll x,y,z;
        tie(x,y,z)=pq.top();
        pq.pop();
        if(vis[y][z]==1) continue;
        vis[y][z]=1;
        for(auto i:adj[y])
        {
            if(dis[i.F][z]>dis[y][z]+i.S)
            {
                dis[i.F][z]=dis[y][z]+i.S;
                pq.push({-dis[i.F][z],i.F,z});
            }
            if(z<k)
            {
                if(dis[i.F][z+1]>dis[y][z])
                {
                    dis[i.F][z+1]=dis[y][z];
                    pq.push({-dis[i.F][z+1],i.F,z+1});
                }
            }
        }
    }
    if(dis[p][q]==hell) cout<<-1;
    else cout<<dis[p][q];
    // for(int i=1;i<=n;i++)
    // {
        // ll ans=hell;
        // for(int j=0;j<=k;j++) ans=min(ans,dis[i][j]);
        // cout<<ans<<' ';
    // }
    return 0;
}