#include <bits/stdc++.h> 

using namespace std;

typedef long long ll;
typedef long double ld;


const int N = (int)3e3 + 12, MOD = (int)1e9 + 7;


int n, s;

struct pt{
    int x, y;
};
void in(pt &a) {
    cin >> a.x >> a.y;
}
vector<array<pt, 2>> a;

ld dist(pt a, pt b) {
    ld x = (a.x - b.x) ,y = (b.x - a.y);
    return sqrtl(x * x + y * y);
}
ld get(pt x, pt y) {
    return min(dist(a[0][0], x) + dist(a[0][1], y), dist(a[0][1], x) + dist(a[0][0], y)) + s * 4;
}
void test() {
    cin >> n >> s;
    a.resize(n);
    for(int i = 0; i < n; i++) {
        in(a[i][0]);in(a[i][1]);
    }
    ld res = s * 8;
    res = min({res, get({-s, -s}, {s, s}), get({-s, s}, {s, -s})});
    // cout << get({-s, -s}, {s, s}) << '\n';
    cout << fixed << setprecision(7) << res << '\n';
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    int t = 1;
    // cin >> t;

    while(t--) 
        test();

    return 0;
}