#include <bits/stdc++.h> 
#include <ext/pb_ds/assoc_container.hpp> 
using namespace std;
using namespace __gnu_pbds;
// Policy based data structure 
typedef tree<int, null_type, 
			less_equal<int>, rb_tree_tag, 
			tree_order_statistics_node_update> 
	indexed_set;  
#define ll long long int
#define pii pair<ll,ll>
#define rep(i, begin, end) for (__typeof(end) i = (begin) - ((begin) > (end)); i != (end) - ((begin) > (end)); i += 1 - 2 * ((begin) > (end)))
#define vi vector<ll>
#define vii vector<pii>
#define all(x) x.begin(),x.end()
#define eb emplace_back
#define yes cout<<"YES"<<endl; return;
#define no cout<<"NO"<<endl; return;
#define flus fflush(stdin); fflush(stdout);
#define F first
#define S second
#define np next_permutation
#define inf 1e18
#define mod 1000000007
#define N 1005
#define pi (double)2*acos(0.0)
#define minpq priority_queue <ll, vector<ll>, greater<ll>>
#define maxpq priority_queue<ll> 
/*******************************************************************/
struct state{
	ll dist,node,used;
	state(ll dist1,ll node1,ll used1){
		dist=dist1;
		node=node1;
		used=used1;
	}
	bool operator<(const state&s) const{
		if(this->dist==s.dist){
			if(this->node==s.node){
				return this->used < s.used;
			} else{
				return this->node < s.node;
			}
		} else{
			return this->dist < s.dist;
		}
	}
};
ll n,m,a,b,k;
vii adj[N];
ll dist[N][N];
void solve(){
	cin>>n>>m>>a>>b>>k;
	rep(i,0,m){
		ll u,v,w;
		cin>>u>>v>>w;
		adj[u].eb(v,w);
		adj[v].eb(u,w);
	}
	rep(i,0,n+1){
		rep(j,0,k+1){
			dist[i][j]=inf;
		}
	}
	rep(i,0,k+1){
		dist[a][i]=0;
	}
	map<pii,pii> pa;
	set<state> s;
	s.insert(state(0,a,0));
	while(!s.empty()){
		state curr=*s.begin();
		// curr.print();
		s.erase(s.begin());
		for(auto ch:adj[curr.node]){
			if(dist[ch.F][curr.used]>dist[curr.node][curr.used] + ch.S){
				state temp(dist[ch.F][curr.used],ch.F,curr.used);
				auto it=s.find(temp);
				if(it!=s.end())
					s.erase(it);
				dist[ch.F][curr.used]=dist[curr.node][curr.used] + ch.S;
				pa[{ch.F,curr.used}]={curr.node,curr.used};
				temp.dist=dist[ch.F][curr.used];
				s.insert(temp);
			}
			if(curr.used+1<=k and dist[ch.F][curr.used+1]>dist[curr.node][curr.used]){
				state temp(dist[ch.F][curr.used+1],ch.F,curr.used+1);
				auto it=s.find(temp);
				if(it!=s.end())
					s.erase(it);
				dist[ch.F][curr.used+1]=dist[curr.node][curr.used];
				pa[{ch.F,curr.used+1}]={curr.node,curr.used};
				temp.dist=dist[ch.F][curr.used+1];
				s.insert(temp);
			}
		}
	}
	ll ans=inf;
	rep(i,0,k+1){
		ans=min(ans,dist[b][i]);
	}
	if(ans>=inf){
		cout<<-1<<endl;
	} else{
		cout<<ans<<endl;
	}
}

int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	int t;
	// cin>>t;
	t=1;
	while(t--){
		solve();
	}
}