#include<bits/stdc++.h>

using namespace std;

typedef long long int ll;

const int maxn = 1e5+;

const int INF = 0x3f3f3f3f;

struct State

{

    // 优先队列的结点结构体

    int v, w, cnt; // cnt 表示已经使用多少次免费通行权限

    State() {}

    State(int v, int w, int cnt) : v(v), w(w), cnt(cnt) {}

    bool operator<(const State &rhs) const

    {

        return w > rhs.w;

    }

};

struct node

{

    int v;

    int w;

    int next;

    /* data */

} edge[maxn];

priority_queue<State>pq;

int n,t,m,k,u,v,w,s;

int cnt;

bool vis[maxn][];

int dis[maxn][];

int head[maxn];

void add(int u,int v,int w)     //链式前向星存边

{

    edge[cnt] = {v,w,head[u]};

    head[u] = cnt++;

}

void dijkstra()

{

    memset(dis, 0x3f, sizeof(dis));

    dis[s][] = ;

    pq.push(State(s, , )); // 到起点不需要使用免费通行权，距离为零

    while (!pq.empty())

    {

        State top = pq.top();

        pq.pop();

        int u = top.v;

        int nowCnt = top.cnt;

        if (vis[u][nowCnt])

            continue;

        vis[u][nowCnt] = true;

        for (int i = head[u]; ~i; i = edge[i].next)

        {

            int v = edge[i].v, w = edge[i].w;

            if (nowCnt < k && dis[v][nowCnt + ] > dis[u][nowCnt])

            {

                // 可以免费通行

                dis[v][nowCnt + ] = dis[u][nowCnt];

                pq.push(State(v, dis[v][nowCnt + ], nowCnt + ));

            }

            if (dis[v][nowCnt] > dis[u][nowCnt] + w)

            {

                // 不可以免费通行

                dis[v][nowCnt] = dis[u][nowCnt] + w;

                pq.push(State(v, dis[v][nowCnt], nowCnt));

            }

        }

    }

}

int main()

{

    memset(head,-,sizeof (head));

    scanf("%d%d%d%d%d",&n,&m,&s,&t,&k);

    while (m--)

    {

        scanf("%d%d%d",&u,&v,&w);

        add(u, v, w);

        add(v, u, w);

    }

    int ans = INF;

    dijkstra();

    for (int i = ; i <= k; ++i)

        ans = min(ans, dis[t][i]); // 对到达终点的所有情况取最优值

    cout << ans << endl;

}