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

#define rep(i, b, e) for (int i = (b); i <= (e); i++)
#define per(i, b, e) for (int i = (e); i >= (b); i--)
#define FOR(i, b, e) rep(i, b, (e)-1)
#define SZ(x) int(x.size())
#define all(x) x.begin(), x.end()
#define pb push_back
#define mp make_pair
#define st first
#define nd second
using ll = long long;
using vi = vector<int>;
using pii = pair<int, int>;

auto& operator<<(auto& o, pair<auto, auto> p) {
  return o << "(" << p.st << ", " << p.nd << ")";
}
auto operator<<(auto& o, auto x) -> decltype(end(x), o) {
  o << "{";
  int i = 0;
  for (auto e : x)
    o << ", " + 2 * !i++ << e;
  return o << "}";
}
#ifdef LOCAL
#define deb(x...)                       \
  cerr << "[" #x "]: ", [](auto... $) { \
    ((cerr << $ << "; "), ...) << endl; \
  }(x)
#else
#define deb(...)
#endif

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

  int n, c;
  cin >> n >> c;

  vector<ll> best_ans(500333), temp(500333);
  ll ans = 0;
  vi a(n), w(n);

  for (int i = 0; i < n; i++) {
    cin >> a[i] >> w[i];
  }

  for (int i = 0; i < n;) {
    int idx = i;
    while (idx < n && a[idx] == a[i]) {
      // cout << idx << ": ";
      temp[w[idx]] = max(best_ans[w[idx]] + a[idx], ans + a[idx] - c);
      // cout << temp[w[idx]] << " " << best_ans[w[idx]] + a[idx] << "\n";
      idx++;
    }
    idx = i;
    while (idx < n && a[idx] == a[i]) {
      ans = max(ans, temp[w[idx]]);
      best_ans[w[idx]] = max(best_ans[w[idx]], temp[w[idx]]);
      idx++;
    }
    i = idx;
  }

  cout << ans << "\n";
}