// #pragma GCC optimize("Ofast,no-stack-protector")
// #pragma GCC optimize("O3,unroll-loops")
// #pragma GCC target("avx,avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>
#define lowbit(x) ((x) & -(x))
#define ml(a, b) ((1ll * (a) * (b)) % M)
#define tml(a, b) (a) = ((1ll * (a) * (b)) % M)
#define ad(a, b) ((0ll + (a) + (b)) % M)
#define tad(a, b) (a) = ((0ll + (a) + (b)) % M)
#define mi(a, b) ((0ll + M + (a) - (b)) % M)
#define tmi(a, b) (a) = ((0ll + M + (a) - (b)) % M)
#define tmin(a, b) (a) = min((a), (b))
#define tmax(a, b) (a) = max((a), (b))
#define iter(a) (a).begin(), (a).end()
#define riter(a) (a).rbegin(), (a).rend()
#define init(a, b) memset((a), (b), sizeof(a))
#define cpy(a, b) memcpy((a), (b), sizeof(a))
#define uni(a) a.resize(unique(iter(a)) - a.begin())
#define size(x) (int)x.size()
#define pb emplace_back
#define mpr make_pair
#define ls(i) ((i) << 1)
#define rs(i) ((i) << 1 | 1)
#define INF 0x3f3f3f3f
#define NIF 0xc0c0c0c0
#define eps 1e-9
#define F first
#define S second
#define AC cin.tie(0)->sync_with_stdio(0)
using namespace std;
typedef long long llt;
typedef __int128_t lll;
typedef pair<int, int> pii;
typedef pair<double, double> pdd;
typedef pair<llt, llt> pll;
typedef pair<llt, int> pli;
typedef complex<double> cd;
// const int M = 998244353;
// random_device rm;
// mt19937 rg(rm());
// default_random_engine rg(rm());
// uniform_int_distribution<int> rd(INT_MIN, INT_MAX);
// uniform_real_distribution<double> rd(0, M_PI);
void db() { cerr << "\n"; }
template <class T, class... U>
void db(T a, U... b) { cerr << a << " ", db(b...); }
inline char gc()
{
const static int SZ = 1 << 16;
static char buf[SZ], *p1, *p2;
if (p1 == p2 && (p2 = buf + fread(p1 = buf, 1, SZ, stdin), p1 == p2))
return -1;
return *p1++;
}
void rd() {}
template <typename T, typename... U>
void rd(T &x, U &...y)
{
x = 0;
bool f = 0;
char c = gc();
while (!isdigit(c))
f ^= !(c ^ 45), c = gc();
while (isdigit(c))
x = (x << 1) + (x << 3) + (c ^ 48), c = gc();
f && (x = -x), rd(y...);
}
template <typename T>
void prt(T x)
{
if (x < 0)
putchar('-'), x = -x;
if (x > 9)
prt(x / 10);
putchar((x % 10) ^ 48);
}
typedef pair<double, int> pdl;
double solve(int n, int m, int k, int H, std::vector<int> x, std::vector<int> y, std::vector<int> c, std::vector<int> ar)
{
vector<pii> eg[n];
for (int i = 0; i < m; i++)
eg[x[i]].pb(c[i], y[i]), eg[y[i]].pb(c[i], x[i]);
vector<double> ans(n, 1e18);
vector<bool> vd(n, 0);
{
ans[0] = 0;
queue<int> q;
q.push(0), vd[0] = 1;
while (!q.empty())
{
int u = q.front();
q.pop();
if (u == H)
continue;
if (!ar[u])
ans[u] = 0;
for (pii v : eg[u])
if (!vd[v.S])
q.push(v.S), vd[v.S] = 1;
}
if (!vd[H])
return -1;
}
auto dij = [&]() -> void
{
priority_queue<pdl, vector<pdl>, greater<pdl>> pq;
for (int i = 0; i < n; i++)
if (ans[i] < 1e16)
pq.emplace(ans[i], i);
fill(iter(vd), 0);
while (!pq.empty())
{
pdl tp = pq.top();
pq.pop();
if (vd[tp.S])
continue;
vd[tp.S] = 1;
if (tp.S == H)
continue;
for (pii v : eg[tp.S])
if (!vd[v.S] && ans[tp.S] + v.F < ans[v.S])
pq.emplace(ans[v.S] = ans[tp.S] + v.F, v.S);
}
for (int i = 0; i < n; i++)
if (ar[i] == 2)
ans[i] /= 2.0;
};
for (int t = min(k, 60); t >= 0; t--)
dij();
return ans[H];
}
// signed main()
// {
// int n, m, k, h;
// rd(n, m, k, h);
// vector<int> ar(n), x(m), y(m), c(m);
// for (int i = 0; i < n; i++)
// rd(ar[i]);
// for (int i = 0; i < m; i++)
// rd(x[i], y[i], c[i]);
// cout << solve(n, m, k, h, x, y, c, ar) << '\n';
// }
