#include <bits/stdc++.h>
#define N 5009
using namespace std;
vector<int>to[N];
int n, m, k;
int d[N][N];

void bfs(int st) {
	queue<int>q;
	q.push(st);
	d[st][st] = 0;
	while (!q.empty()) {
		int x = q.front();
		q.pop();
		for (auto y : to[x]) {
			if (d[st][y] != 1000000000)
				continue;
			d[st][y] = d[st][x] + 1;
			q.push(y);
		}
	}
}

double calc(int a, int b, int kt) {
	if (a == 0 && b == 0)
		return 0;
	kt += a + b;
	int ta = max((int)(kt / (a + sqrt(2) * b)) - 2, 1);
	int tb = max((int)(sqrt(2) * ta) - 2, 1);
	//cout << ta << " " << tb << endl;
	double ans = 1.0 * a / ta + 2.0 * b / tb;
	kt -= ta * a + tb * b;
	while (kt) {
		//cout << kt << " " << ta << " " << tb << endl;
		if (1.0 / ta / (ta + 1) > 2.0 / tb / (tb + 1)) {
			ans -= min(kt, a) * 1.0 / ta / (ta + 1);
			kt -= min(kt, a);
			ta++;
		} else {
			ans -= min(kt, b) * 2.0 / tb / (tb + 1);
			kt -= min(kt, b);
			tb++;
		}
	}
	//cout << a << " " << b << " " << k << " " << ans << endl;
	return ans;
}

int main() {
	cin >> n >> m >> k;
	for (int i = 1; i <= m; i++) {
		int a, b;
		cin >> a >> b;
		to[a].push_back(b);
		to[b].push_back(a);
	}
	fill(d[0], d[0] + N * N, 1000000000);
	for (int i = 1; i <= n; i++)
		bfs(i);
	/*
	for (int i = 1; i <= n; i++, cout << endl)
		for (int j = 1; j <= n; j++)
			cout << d[i][j] << " ";
	*/
	int s1, t1, s2, t2;
	cin >> s1 >> t1 >> s2 >> t2;
	double ans = calc(d[s1][t1] + d[s2][t2], 0, k);
	for (int a = 1; a <= n; a++) {
		for (int b = 1; b <= n; b++) {
			if (d[s1][a] == 1000000000 || d[b][t1] == 1000000000 || d[a][b] == 1000000000)
				continue;
			if (d[s2][a] == 1000000000 || d[b][t2] == 1000000000)
				continue;
			ans = min(ans, calc(d[s1][a] + d[b][t1] + d[s2][a] + d[b][t2], d[a][b], k));
		}
	}
	cout << fixed << setprecision(15) << ans;
}