#include <bits/stdc++.h>
using namespace std;
const int N = 3e5 + 7;
const int inf = 0x3f3f3f3f;
const long long INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 998244353;
const double eps = 1e-8;
int Log[N];
struct ST {
  long long dp[N][20];
  int ty;
  void build(int n, long long b[], int _ty) {
    ty = _ty;
    for (int i = 1; i <= n; i++) dp[i][0] = ty * b[i];
    for (int j = 1; j <= Log[n]; j++)
      for (int i = 1; i + (1 << j) - 1 <= n; i++)
        dp[i][j] = max(dp[i][j - 1], dp[i + (1 << (j - 1))][j - 1]);
  }
  long long query(int x, int y) {
    if (x > y) return 0;
    int k = Log[y - x + 1];
    return ty * max(dp[x][k], dp[y - (1 << k) + 1][k]);
  }
};
int n, a, id[N];
int d[N], c[N];
long long ans, prefix[N], suffix[N];
set<int> Set[2];
ST rmq[2];
bool cmp(const int& a, const int& b) {
  return d[a + 1] - d[a] > d[b + 1] - d[b];
}
int main() {
  for (int i = -(Log[0] = -1); i < N; i++)
    Log[i] = Log[i - 1] + ((i & (i - 1)) == 0);
  scanf("%d%d", &n, &a);
  for (int i = 1; i <= n; i++) scanf("%d%d", &d[i], &c[i]);
  for (int i = 1; i <= n; i++) c[i] = a - c[i], ans = max(ans, 1ll * c[i]);
  for (int i = 1; i <= n; i++) id[i] = i;
  for (int i = 1; i <= n; i++) prefix[i] = prefix[i - 1] + c[i];
  for (int i = n; i >= 1; i--) suffix[i] = suffix[i + 1] + c[i];
  rmq[0].build(n, prefix, 1);
  rmq[1].build(n, suffix, 1);
  sort(id + 1, id + n, cmp);
  Set[0].insert(0);
  Set[1].insert(n + 1);
  for (int i = 1; i < n; i++) {
    int x = id[i];
    int L = *(--Set[0].upper_bound(x)) + 1;
    int R = *(Set[1].upper_bound(x + 1)) - 1;
    long long ret = 0;
    ret += rmq[0].query(x + 1, R) - prefix[x];
    ret += rmq[1].query(L, x) - suffix[x + 1];
    ret -= 1ll * (d[x + 1] - d[x]) * (d[x + 1] - d[x]);
    ans = max(ans, ret);
    Set[0].insert(x);
    Set[1].insert(x + 1);
  }
  printf("%lld\n", ans);
  return 0;
}
