#define MOD_TYPE 2

#include <bits/stdc++.h>
using namespace std;

//#include <atcoder/all>
#include <atcoder/modint>
//#include <atcoder/segtree>
using namespace atcoder;

#if 0
#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/cpp_int.hpp>
using Int = boost::multiprecision::cpp_int;
using lld = boost::multiprecision::cpp_dec_float_100;
#endif

#if 0
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tag_and_trait.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>
using namespace __gnu_pbds;
using namespace __gnu_cxx;
template <typename T>
using extset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#endif

#if 1
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#endif

#pragma region Macros

using ll = long long int;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pld = pair<ld, ld>;
template <typename Q_type>
using smaller_queue = priority_queue<Q_type, vector<Q_type>, greater<Q_type>>;

#if MOD_TYPE == 1
constexpr ll MOD = ll(1e9 + 7);
#else
#if MOD_TYPE == 2
constexpr ll MOD = 998244353;
#else
constexpr ll MOD = 1000003;
#endif
#endif

using mint = static_modint<MOD>;
constexpr int INF = (int)1e9 + 10;
constexpr ll LINF = (ll)4e18;
constexpr double PI = acos(-1.0);
constexpr double EPS = 1e-11;
constexpr int Dx[] = {0, 0, -1, 1, -1, 1, -1, 1, 0};
constexpr int Dy[] = {1, -1, 0, 0, -1, -1, 1, 1, 0};

#define REP(i, m, n) for (ll i = m; i < (ll)(n); ++i)
#define rep(i, n) REP(i, 0, n)
#define REPI(i, m, n) for (int i = m; i < (int)(n); ++i)
#define repi(i, n) REPI(i, 0, n)
#define MP make_pair
#define MT make_tuple
#define YES(n) cout << ((n) ? "YES" : "NO") << "\n"
#define Yes(n) cout << ((n) ? "Yes" : "No") << "\n"
#define possible(n) cout << ((n) ? "possible" : "impossible") << "\n"
#define Possible(n) cout << ((n) ? "Possible" : "Impossible") << "\n"
#define Yay(n) cout << ((n) ? "Yay!" : ":(") << "\n"
#define all(v) v.begin(), v.end()
#define NP(v) next_permutation(all(v))
#define dbg(x) cerr << #x << ":" << x << "\n";
#define UNIQUE(v) v.erase(unique(all(v)), v.end())

struct io_init {
  io_init() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << setprecision(30) << setiosflags(ios::fixed);
  };
} io_init;
template <typename T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
inline ll CEIL(ll a, ll b) { return (a + b - 1) / b; }
template <typename A, size_t N, typename T>
inline void Fill(A (&array)[N], const T& val) {
  fill((T*)array, (T*)(array + N), val);
}
template <typename T>
vector<T> compress(vector<T>& v) {
  vector<T> val = v;
  sort(all(val)), val.erase(unique(all(val)), val.end());
  for (auto&& vi : v) vi = lower_bound(all(val), vi) - val.begin();
  return val;
}
template <typename T, typename U>
constexpr istream& operator>>(istream& is, pair<T, U>& p) noexcept {
  is >> p.first >> p.second;
  return is;
}
template <typename T, typename U>
constexpr ostream& operator<<(ostream& os, pair<T, U> p) noexcept {
  os << p.first << " " << p.second;
  return os;
}
ostream& operator<<(ostream& os, mint m) {
  os << m.val();
  return os;
}
ostream& operator<<(ostream& os, modint m) {
  os << m.val();
  return os;
}

random_device seed_gen;
mt19937_64 engine(seed_gen());

struct BiCoef {
  vector<mint> fact_, inv_, finv_;
  BiCoef(int n) noexcept : fact_(n, 1), inv_(n, 1), finv_(n, 1) {
    fact_.assign(n, 1), inv_.assign(n, 1), finv_.assign(n, 1);
    for (int i = 2; i < n; i++) {
      fact_[i] = fact_[i - 1] * i;
      inv_[i] = -inv_[MOD % i] * (MOD / i);
      finv_[i] = finv_[i - 1] * inv_[i];
    }
  }
  mint c(ll n, ll k) const noexcept {
    if (n < k || n < 0 || k < 0) return 0;
    return fact_[n] * finv_[k] * finv_[n - k];
  }
  mint P(ll n, ll k) const noexcept { return c(n, k) * fact_[k]; }
  mint H(ll n, ll k) const noexcept { return c(n + k - 1, k); }
  mint Ch1(ll n, ll k) const noexcept {
    if (n < 0 || k < 0) return 0;
    mint res = 0;
    for (int i = 0; i < n; i++)
      res += c(n, i) * mint(n - i).pow(k) * (i & 1 ? -1 : 1);
    return res;
  }
  mint fact(ll n) const noexcept {
    if (n < 0) return 0;
    return fact_[n];
  }
  mint inv(ll n) const noexcept {
    if (n < 0) return 0;
    return inv_[n];
  }
  mint finv(ll n) const noexcept {
    if (n < 0) return 0;
    return finv_[n];
  }
};

BiCoef bc(500010);

#pragma endregion

void solve() {
  int n, d;
  cin >> n >> d;
  vector<ll> p(n), q(n);
  rep(i, n) cin >> p[i] >> q[i];
  ll Max = -LINF;
  auto itr = min_element(all(p));
  ll pmin = *itr;
  int pmin_i = itr - p.begin();
  ll pmin2 = LINF;
  int pmin_i2;
  rep(i, n) {
    if (i == pmin_i) continue;
    if (chmin(pmin2, p[i])) pmin_i2 = i;
  }
  bool pass = false;
  if (pmin == pmin2 and (p[pmin_i] <= q[pmin_i] or p[pmin_i2] <= q[pmin_i2]))
    pass = true;

  rep(i, n) rep(j, n) {
    if (i == j) continue;
    ll Min = 0;
    if (d % 2 == 0) {
      chmin(Min, -p[i]);
      if (d > 2) chmin(Min, -p[i] + q[i] - p[j]);
      ll s = -p[i] + q[i] - p[j] + q[j];
      if (pass) {
        chmin(Min, s * (d / 2 - 1) - pmin);
      } else {
        chmin(Min, s * (d / 2 - 1) - p[i]);
        if (pmin_i != i)
          chmin(Min, s * (d / 2 - 1) - p[i] + q[i] - pmin);
        else
          chmin(Min, s * (d / 2 - 1) - p[i] + q[i] - pmin2);
      }

    } else {
      chmin(Min, -p[i]);
      chmin(Min, -p[i] + q[i] - p[j]);
      ll s = -p[i] + q[i] - p[j] + q[j];
      chmin(Min, s * ((d - 1) / 2 - 1) - p[i]);
      chmin(Min, s * ((d - 1) / 2 - 1) - p[i] + q[i] - p[j]);
      if (pmin_i != j)
        chmin(Min, s * ((d - 1) / 2 - 1) - p[i] + q[i] - p[j] + q[j] - pmin);
      else
        chmin(Min, s * ((d - 1) / 2 - 1) - p[i] + q[i] - p[j] + q[j] - pmin2);
    }
    chmax(Max, Min);
  }
  cout << Max << "\n";
}

int main() { solve(); }