#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ldb double
#define pb push_back

const int N=5050;
vector<int> E[N];
const ll inf=1e9+7;
ll best[N],dist[N][N];

ldb Calc(int x,int k){
	if(x==0)return 0;
	int val=k/x+1;
	int ost=k%x;
	return (ldb)1/val*(x-ost)+(ldb)1/(val+1)*ost;
}
ldb Calc(int x,int kx,int y,int ky){
	return 2*Calc(x,kx)+Calc(y,ky);
}
int main(){
	int n,m,k;
	scanf("%i %i %i",&n,&m,&k);
	for(int i=1;i<=m;i++){
		int u,v;
		scanf("%i %i",&u,&v);
		E[u].pb(v);
		E[v].pb(u);
	}
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			dist[i][j]=inf;
		}
		dist[i][i]=0;
		queue<int> q;
		q.push(i);
		while(q.size()){
			int u=q.front();
			q.pop();
			for(int v:E[u]){
				if(dist[i][v]>dist[i][u]+1){
					dist[i][v]=dist[i][u]+1;
					q.push(v);
				}
			}
		}
	}
	int s1,t1,s2,t2;
	scanf("%i %i %i %i",&s1,&t1,&s2,&t2);
	best[0]=dist[s1][t1]+dist[s2][t2];
	for(int i=1;i<n;i++)best[i]=inf;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			if(j!=i && dist[i][j]!=inf){
				ll now=min(dist[s1][i]+dist[s2][i]+dist[t1][j]+dist[t2][j],dist[s1][i]+dist[s2][j]+dist[t1][j]+dist[t2][i]);
				best[dist[i][j]]=min(best[dist[i][j]],now);
			}
		}
	}
	ldb ans=best[0];
	for(int i=0;i<n;i++){
		if(best[i]<inf){
			int bot=0,top=k-1,sol=k;
			while(bot<=top){
				int mid=bot+top>>1;
				ldb ans1=Calc(i,mid,best[i],k-mid);
				ldb ans2=Calc(i,mid+1,best[i],k-mid-1);
				if(ans1<ans2){
					top=mid-1;
					sol=mid;
				}else{
					bot=mid+1;
				}
			}
			ans=min(ans,Calc(i,sol,best[i],k-sol));
		}
	}
	printf("%.12lf\n",ans);
	return 0;
}