#include <bits/stdc++.h>

using namespace std;

const int N = 2e5 + 5, C = 18;

int n, m, col[N];
double P, a[C + 5];
vector<int> G[N];
vector< pair<int, int> > E;
double f[N], g[N];
int wf[N];

void dfs(int x, int fa = -1) {
    double h[C + 5];
    for (int i = 1; i <= C; ++i) h[i] = a[i];
    if (col[x]) {
        for (int i = 1; i <= C; ++i) {
            if ((i == abs(col[x])) != (col[x] > 0)) h[i] = -1e9;
        }
    }
    for (auto v : G[x]) {
        if (v == fa) continue;
        dfs(v, x);
        for (int i = 1; i <= C; ++i) {
            h[i] += (i == wf[v] ? g : f)[v];
        }
    }
    wf[x] = max_element(h + 1, h + C + 1) - h;
    f[x] = h[wf[x]], g[x] = -1e9;
    for (int i = 1; i <= C; ++i) {
        if (i != wf[x]) g[x] = max(g[x], h[i]);
    }
}

int check(double res) {
    if (E.empty()) {
        dfs(1);
        return f[1] > res;
    }
    if (E.size() == 1) {
        for (int i = 1; i <= C; ++i) {
            for (int j = 1; j <= n; ++j) {
                if (j == E[0].first) col[j] = i;
                else if (j == E[0].second) col[j] = -i;
                else col[j] = 0;
            }
            dfs(1);
            if (f[1] > res) return 1;
        }
        return 0;
    }
    dfs(1);
    return (f[1] > res);
}

signed main() {
    scanf("%d%d", &n, &m);
    for (int i = 1, x, y; i < n; ++i) {
        scanf("%d%d", &x, &y);
        G[x].push_back(y);
        G[y].push_back(x);
    }
    for (int i = 1, x, y; i <= m; ++i) {
        scanf("%d%d", &x, &y);
        E.push_back({x, y});
    }
    scanf("%lf", &P);
    double L = 0, R = n / (1 + P / n), res = 0;
    while (fabs(L - R) > 1e-5) {
        double mid = (L + R) / 2;
        for (int i = 1; i <= C; ++i) {
            a[i] = ((double)1 / i - mid * P * i);
        }
        if (check(mid)) {
            res = mid, L = mid;
        } else {
            R = mid;
        }
    }
    printf("%.3lf\n", res);
    return 0;
}