#include <bits/stdc++.h>
using namespace std;
const int N = 300100;
int n;
long long d[N], c[N], pref[N], dp[N], a;
long long ans = 0;
long long t[N * 4], ob[N * 4];
void push(int v) {
  if (ob[v] == 0) return;
  t[v + v] += ob[v];
  t[v + v + 1] += ob[v];
  ob[v + v] += ob[v];
  ob[v + v + 1] += ob[v];
  ob[v] = 0;
}
void update(int v, int l, int r, int tl, int tr, long long x) {
  if (l > r || tl > r || l > tr || tl > tr) return;
  if (tl <= l && r <= tr) {
    t[v] += x;
    ob[v] += x;
    return;
  }
  int mid = (l + r) >> 1;
  push(v);
  update(v + v, l, mid, tl, tr, x);
  update(v + v + 1, mid + 1, r, tl, tr, x);
  t[v] = max(t[v + v], t[v + v + 1]);
}
long long get(int v, int l, int r, int tl, int tr) {
  if (l > r || tl > r || l > tr || tl > tr) return -1e15;
  if (tl <= l && r <= tr) {
    return t[v];
  }
  push(v);
  int mid = (l + r) >> 1;
  return max(get(v + v, l, mid, tl, tr), get(v + v + 1, mid + 1, r, tl, tr));
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> a;
  for (int i = 1; i <= n; i++) {
    cin >> d[i] >> c[i];
    pref[i] = pref[i - 1] + (a - c[i]);
  }
  stack<pair<long long, long long> > stck;
  update(1, 1, n, 1, 1, a - c[1]);
  ans = max(ans, a - c[1]);
  stck.push({1e18, 1});
  for (int i = 2; i <= n; i++) {
    ans = max(ans, a - c[i]);
    update(1, 1, n, 1, i, a - c[i]);
    long long cur = (d[i] - d[i - 1]) * (d[i] - d[i - 1]);
    while (!stck.empty() && stck.top().first <= cur) {
      int pos = stck.top().second;
      long long x = stck.top().first;
      stck.pop();
      int lst = stck.top().second;
      update(1, 1, n, lst, pos - 1, x);
    }
    update(1, 1, n, stck.top().second, i - 1, -cur);
    ans = max(ans, get(1, 1, n, 1, i - 1));
    stck.push({cur, i});
  }
  cout << ans;
}
