#include <bits/stdc++.h>

using i64 = long long;

struct Point {
    int x = 0;
    int y = 0;
};

Point operator-(const Point &a, const Point &b) {
    return {a.x - b.x, a.y - b.y};
}

Point operator-(const Point &a) {
    return {-a.x, -a.y};
}

Point rotate(const Point &a) {
    return {-a.y, a.x};
}

i64 cross(const Point &a, const Point &b) {
    return 1LL * a.x * b.y - 1LL * a.y * b.x;
}

i64 dot(const Point &a, const Point &b) {
    return 1LL * a.x * b.x + 1LL * a.y * b.y;
}

bool operator<(const Point &a, const Point &b) {
    return cross(a, b) > 0;
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    
    int n, d;
    std::cin >> n >> d;
    
    std::vector<Point> a(n + 2);
    a[0] = Point(0, 0);
    a[1] = Point(d, 0);
    for (int i = 2; i < n + 2; i++) {
        std::cin >> a[i].x >> a[i].y;
    }
    
    std::vector dp(n + 2, std::vector<i64>(n + 2, -4E18));
    dp[0][1] = 0;
    
    std::vector<std::tuple<Point, int, int>> e;
    for (int i = 0; i < n + 2; i++) {
        for (int j = 0; j < n + 2; j++) {
            if (cross(a[i], a[j]) < 0) {
                continue;
            }
            if (((a[i].y <= 0 && a[j].y <= 0) || (a[i].y >= 0 && a[j].y >= 0)) && a[i].x != a[j].x) {
                Point v = rotate(a[j] - a[i]);
                if (v.y < 0) {
                    v = -v;
                }
                e.emplace_back(v, i, j);
            }
        }
    }
    
    std::vector ok(n + 2, std::vector<bool>(n + 2));
    for (int i = 0; i < n + 2; i++) {
        for (int j = 0; j < n + 2; j++) {
            ok[i][j] = dot(a[i] - a[j], a[i] - a[j]) <= 1LL * d * d;
        }
    }
    
    std::sort(e.begin(), e.end());
    for (auto [v, i, j] : e) {
        if (a[i].y <= 0 && a[j].y <= 0) {
            for (int k = 0; k < n + 2; k++) {
                if (ok[i][k] && ok[j][k]) {
                    dp[j][k] = std::max(dp[j][k], dp[i][k] + cross(a[i], a[j]));
                }
            }
        }
        
        if (a[i].y >= 0 && a[j].y >= 0) {
            for (int k = 0; k < n + 2; k++) {
                if (ok[k][i] && ok[k][j]) {
                    dp[k][j] = std::max(dp[k][j], dp[k][i] + cross(a[i], a[j]));
                }
            }
        }
    }
    
    std::cout << dp[1][0] << "\n";
    
    return 0;
}