#include <bits/stdc++.h>

using namespace std;

const int N = 2005;

vector< pair<int, long long> > G[N];
long double f[N][N];

signed main() {
    int n, m, T; scanf("%d%d%d", &n, &m, &T);
    for (int i = 1, x, y, z, v; i <= m; ++i) {
        scanf("%d%d%d%d", &x, &y, &z, &v);
        G[x].push_back({y, 1ll * z * v});
        G[y].push_back({x, 1ll * z * v});
    }
    for (int i = 1; i <= n; ++i) {
        for (int j = 0; j <= n; ++j) f[i][j] = 1e18;
    }
    f[1][0] = 0;
    for (int i = 0; i < n; ++i) {
        for (int j = 1; j <= n; ++j) {
            for (auto [x, y] : G[j]) {
                f[x][i + 1] = min(f[x][i + 1], f[j][i] + sqrt(y));
            }
        }
    }
    long double res = 1e18;
    for (int i = 0; i <= n; ++i) {
        if (f[n][i] < 1e17) res = min(res, (long double)f[n][i] * f[n][i]);
    }
    printf("%.10Lf\n", res / T);
    return 0;
}