#include <bits/stdc++.h>

#define FOR(i,a,b) for(int i= (a); i<((int)b); ++i)
#define RFOR(i,a) for(int i=(a); i >= 0; --i)
#define FOE(i,a) for(auto i : a)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v,x) (std::find(v.begin(), v.end(), x) != v.end())
#define BIT_ON(bit, i) (((bit >> i) & 1) > 0)
#define BIT_COUNT(bit) (__builtin_popcount(bit))

typedef long long LL;
template<typename T> std::vector<T> make_v(size_t a){return std::vector<T>(a);}
template<typename T,typename... Ts> auto make_v(size_t a, Ts... ts){ return std::vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));}    // C++14
template<typename T,typename V> typename std::enable_if<std::is_class<T>::value==0>::type fill_v(T &t,const V &v){t=v;}
template<typename T,typename V> typename std::enable_if<std::is_class<T>::value!=0>::type fill_v(T &t,const V &v){for(auto &e:t) fill_v(e,v);}
template<class T> inline T ceil(T a, T b) { return (a + b - 1) / b; }
template<class T> inline void print(T x) { std::cout << x << std::endl; }
template<class T> inline void print_vec(const std::vector<T> &v) { for (int i = 0; i < v.size(); ++i) {  if (i != 0) {std::cout << " ";} std::cout << v[i];} std::cout << "\n"; }
inline bool inside(long long y, long long x, long long H, long long W) {return 0 <= y and y < H and 0 <= x and x < W; }
template<class T> inline double euclidean_distance(T y1, T x1, T y2, T x2) { return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)); }
template<class T> inline double manhattan_distance(T y1, T x1, T y2, T x2) { return abs(x1 - x2) + abs(y1 - y2); }
template<typename T> T &chmin(T &a, const T &b) { return a = std::min(a, b); }
template<typename T> T &chmax(T &a, const T &b) { return a = std::max(a, b); }

template<class T> inline std::vector<T> unique(std::vector<T> v) {
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    return v;
}
// 初項s, 交差dのn個の数列の和
long long sum_of_arithmetic_progression(long long s, long long d, long long n) {
    return n * (2 * s + (n - 1) * d) / 2;
}

// 2のべき乗数かどうか
bool is_power_of_two(long long x) {
    return !(x & (x - 1));
}

// aとbの最大公約数 O(log min(a, b))
long long gcd(long long a, long long b) {
    if (b == 0) { return a; }
    return gcd(b, a % b);
}

// 数列vの最大公約数 O(N log d)
long long gcd(std::vector<long long> &v) {
    long long ans = v[0];
    for (int i = 1; i < (int)v.size(); ++i) {
        ans = gcd(ans, v[i]);
    }
    return ans;
}

// aとbの最小公倍数 O(log min(a, b))
long long lcm(long long a, long long b) {
    long long g = gcd(a, b);
    return a / g * b;
}

const int INF = 1u << 30u;
const long long LINF = 1ull << 60u;
const double EPS = 1e-9;
const long double PI = acos(-1.0);
const std::vector<int> dy2 = {0, 1}, dx2 = {1, 0};  // 右，下
const std::vector<int> dy4 = {0, 1, 0, -1}, dx4 = {1, 0, -1, 0};    // 右，下，左，上
const std::vector<int> dy8 = { 0, -1, 0, 1, 1, -1, -1, 1 }, dx8 = { 1, 0, -1, 0, 1, 1, -1, -1 };

using namespace std;

template <typename T> class SegmentTree {
    const int array_size;        // もとの配列のサイズ
    int n;
    std::vector<T> data;
    std::function<T (T,T)> op;
    T unit;

public:
    enum Mode {
        RangeMinimumQuery,
        RangeMaximumQuery,
        RangeSummationQuery,
    };

    SegmentTree(int array_size, Mode mode) : array_size(array_size) {
        if (mode == RangeMinimumQuery) {
            unit = INT_MAX;
            op = [](T a, T b) { return std::min(a, b); };
        }
        else if (mode == RangeMaximumQuery) {
            unit = 0;
            op = [](T a, T b) { return std::max(a, b); };
        }
        else if (mode == RangeSummationQuery) {
            unit = 0;
            op = [](T a, T b) { return a + b; };
        }
        else {
            assert(false);
        }

        n = 1;
        while (n < array_size) { n *= 2; }   // _n以上の最小の2冪
        data.resize(2 * n - 1, unit);
    }

    template <typename F> SegmentTree(int array_size, T unit, F op) : array_size(array_size), unit(unit), op(op) {
        while (n < array_size) { n *= 2; }   // _n以上の最小の2冪
        data.resize(2 * n - 1, unit);
    }

    T access(int idx) {
        return data[idx + n - 1];
    }

    // array[idx] = x
    // O(log N)
    void update(int idx, T x) {
        assert(0 <= idx and idx < array_size);
        idx += n - 1;   // 木での対象のインデックス
        data[idx] = x;
        while (idx > 0) {
            idx = (idx - 1) / 2;                                    // 親のインデックス
            data[idx] = op(data[idx * 2 + 1], data[idx * 2 + 2]);   // 左の子と右の子
        }
    }

    // op(array[left, right))
    // O(log N)
    T query(int left, int right) {
        assert(0 <= left and left < right and right <= array_size);
        return query(left, right, 0, 0, n);
    }

private:
    // [a, b)の目的値をノードk（区間[l, r]）から検索
    T query(int a, int b, int k, int l, int r) {
        assert(a < b && l < r);
        // 範囲外
        if (r <= a || b <= l) {
            return unit;
        }
        // 完全に含む
        if (a <= l && r <= b) {
            return this->data[k];
        }
            // 一部含む
        else {
            T vl = query(a, b, k * 2 + 1, l, (l + r) / 2);    // 左の子
            T vr = query(a, b, k * 2 + 2, (l + r) / 2, r);    // 右の子
            return op(vl, vr);
        }
    }
};



void dfs(int i, int n, const vector<pair<LL, LL>> &v, LL x, LL y, vector<pair<LL, LL>> &res) {
    if (i >= n) {
        res.emplace_back(make_pair(x, y));
        return;
    }

    // not use
    dfs(i + 1, n, v, x, y, res);

    // use a
    dfs(i + 1, n, v, x + v[i].first, y - v[i].second, res);

    // use b
    dfs(i + 1, n, v, x - v[i].first, y + v[i].second, res);
}

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

    LL N, D;
    cin >> N >> D;

    auto v = make_v<pair<LL, LL>>(N);
    FOR(i, 0, N) {
        cin >> v[i].first >> v[i].second;
    }

    int n = N / 2;
    vector<pair<LL, LL>> res1, res2;
    dfs(0, n, v, 0, 0, res1);
    dfs(n, N, v, 0, 0, res2);

    sort(ALL(res1));
    sort(ALL(res2));

    SegmentTree<LL> st(res2.size(), SegmentTree<LL>::RangeMaximumQuery);
    FOR(i, 0, res2.size()) {
        st.update(i, res2[i].second);
    }

    LL ans = 0;
    FOR(i, 0, res1.size()) {
        LL x, y;
        tie(x, y) = res1[i];

        LL left = -D - x;
        LL right = D - x;
        int l = distance(res2.begin(), lower_bound(ALL(res2), make_pair(left, LONG_LONG_MIN)));
        int r = distance(res2.begin(), upper_bound(ALL(res2), make_pair(right, LONG_LONG_MAX)));

        if (l < r) {
            chmax(ans, st.query(l, r) + y);
        }
    }
    print(ans);

    return 0;
}




Measured memory_bytes: 713544