#include <bits/stdc++.h>
using namespace std;
const int N = int(3e5) + 99;
struct node {
  long long sum, ans, pref, suf;
  node() {}
  node(int x) {
    sum = x;
    x = max(x, 0);
    pref = suf = ans = x;
  }
};
node merge(const node &a, const node &b) {
  node res;
  res.sum = a.sum + b.sum;
  res.pref = max(a.pref, a.sum + b.pref);
  res.suf = max(b.suf, b.sum + a.suf);
  res.ans = max(max(a.ans, b.ans), a.suf + b.pref);
  return res;
}
int n, x;
pair<int, int> p[N];
node t[N * 4];
void upd(int v, int l, int r, int pos, int x) {
  if (r - l == 1) {
    assert(pos == l);
    t[v] = node(x);
    return;
  }
  int mid = (l + r) / 2;
  if (pos < mid)
    upd(v * 2 + 1, l, mid, pos, x);
  else
    upd(v * 2 + 2, mid, r, pos, x);
  t[v] = merge(t[v * 2 + 1], t[v * 2 + 2]);
}
node get(int v, int l, int r, int L, int R) {
  if (L >= R) return node(0);
  if (l == L && r == R) return t[v];
  int mid = (l + r) / 2;
  return merge(get(v * 2 + 1, l, mid, L, min(mid, R)),
               get(v * 2 + 2, mid, r, max(L, mid), R));
}
int main() {
  scanf("%d %d", &n, &x);
  for (int i = 0; i < n; ++i) {
    scanf("%d %d", &p[i].first, &p[i].second);
    p[i].second = x - p[i].second;
  }
  sort(p, p + n);
  for (int i = 0; i < n; ++i) upd(0, 0, n, i, p[i].second);
  vector<pair<int, int> > v;
  for (int i = 1; i < n; ++i) v.emplace_back(p[i].first - p[i - 1].first, i);
  sort(v.begin(), v.end());
  long long res = 0;
  set<pair<int, int> > s;
  for (int i = 0; i < n; ++i) {
    s.insert(make_pair(i, i + 1));
    res = max(res, 1LL * p[i].second);
  }
  int l = 0;
  while (l < v.size()) {
    int r = l + 1;
    while (r < v.size() && v[l].first == v[r].first) ++r;
    long long d = v[l].first * 1LL * v[l].first;
    for (int i = l; i < r; ++i) {
      int id = v[i].second;
      auto it = s.upper_bound(make_pair(id, -1));
      assert(it->first == id);
      assert(it != s.begin());
      auto R = *it;
      --it;
      auto L = *it;
      s.erase(L), s.erase(R);
      L.second = R.second;
      auto nd = get(0, 0, n, L.first, L.second);
      res = max(res, nd.ans - d);
      s.insert(L);
    }
    l = r;
  }
  cout << res << endl;
  return 0;
}
