// Problem : Shortest Path Revisited
// Contest : HackerEarth - Algorithms - Graphs - Shortest Path Algorithms
// URL : https://www.hackerearth.com/practice/algorithms/graphs/shortest-path-algorithms/practice-problems/algorithm/shortest-path-revisited-9e1091ea/
// Memory Limit : 256 MB
// Time Limit : 3000 ms
// Powered by CP Editor (https://github.com/cpeditor/cpeditor)

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

int main()
{
    ll n,m,k,hell=1e8,a,b;
    cin>>n>>m>>a>>b>>k;
    vector<pair<ll,ll> > adj[n+1];
    ll dis[n+1][k+1];
    bool vis[n+1][k+1];
    memset(vis,0,sizeof(vis));
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<=k;j++)
        {
            dis[i][j]=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[a][i]=0;
    priority_queue<pair<int,pair<int,int> > >pq;
    pq.push({0,{a,0}});
    while(!pq.empty())
    {
        auto p=pq.top();
        ll x,y,z;
        x=p.F;
        y=p.S.F;
        z=p.S.S;
        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}});
                }
            }
        }
    }
    ll ans=hell;
    for(int i=0;i<=k;i++) ans=min(ans,dis[b][i]);
    if(ans==hell) cout<<-1;
    else cout<<ans;
    return 0;
}