#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double db;
typedef array<ll,2> pr;
const int N = 2010;
const db INF = 1e23L;
template<typename T>void tomin(T& x,T y){x = min(x,y);}
template<typename T>void tomax(T& x,T y){x = max(x,y);}
//
int n,m,T; 

vector<pr> e[N];

db dis[N]; int inq[N];
queue<int> qu;

int main(){
    ios::sync_with_stdio(false); cin.tie(0);
    cin>>n>>m>>T;
    for(int i=1,u,v,x,y;i<=m;i++){
        cin>>u>>v>>x>>y;
        e[u].push_back({v,1ll*x*y});
        e[v].push_back({u,1ll*x*y});
    }
    for(int i=1;i<=n;i++)dis[i] = INF;
    for(auto [v,w] : e[1]){
        tomin(dis[v],(db)w);
        if(!inq[v])qu.push(v),inq[v] = 1;
    }
    while(qu.size()){
        int u = qu.front(); qu.pop(); inq[u] = 0;
        for(auto [v,c] : e[u]){
            db p = sqrt(dis[u]),q = sqrt(c);
            db w = (dis[u]*q + c*p)*(p+q)/p/q;
            if(w < dis[v]){
                dis[v] = w;
                if(!inq[v])qu.push(v),inq[v] = 1;
            }
        }
    }
    db ans = dis[n] / T;
    printf("%.6Lf\n",ans);
    return 0;
}