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#include <bits/stdc++.h>

using namespace std;

#define _DEBUG
#ifdef _DEBUG
template<typename T1, typename T2> auto& operator<<(ostream& o, pair<T1, T2> a) { return o << "(" << a.first << ", " << a.second << ")"; }
template<typename T, typename OS> auto& operator<<(OS& o, T a) { o << "{"; for(auto b : a) o << b << ", "; return o << "}"; }
#define dbg(x...) cerr << "[" #x "]: ", [](auto... args) { ((cerr << args << ", "),...) << "\n"; }(x)
#else
#define dbg(...)
#endif

#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define F first
#define S second

using ll = long long;
using ld = long double;
using pll = pair<ll,ll>;
using vi = vector<int>;

vector<ll> getNextSameW(const vector<ll>& ws, const vector<ll>& as) {
  vector<ll> ans(ws.size(), -1);
  map<ll, ll> pos;
  map<pll, ll> already;
  for(ll i = ws.size() - 1; i >= 0; i--) {
    if(already.count({ws[i], as[i]})) {
      ans[i] = already[{ws[i], as[i]}];
      continue;
    }
    if(pos.count(ws[i])) {
      ans[i] = pos[ws[i]];
    }
    pos[ws[i]] = i;
    already[{ws[i], as[i]}] = ans[i];
  }
  return ans;
}

vector<ll> getNextSmaller(const vector<ll>& as) {
  vector<ll> ans(as.size(), -1);
  for(ll i = as.size() - 2; i >= 0; i--) {
    if(as[i] == as[i + 1]) {
      ans[i] = ans[i + 1];
    }
    else {
      ans[i] = i + 1;
    }
  }
  return ans;
}

ll getScore(ll n, ll c, const vector<ll>& ws, const vector<ll>& as, uint32_t mask) {
  vector<ll> takenAs;
  vector<ll> takenWs;
  for(int i = 0; i < n; i++) {
    if((1 << i) & mask) {
      takenAs.push_back(as[i]);
      takenWs.push_back(ws[i]);
    }
  }

  ll ans = 0;
  for(int i = 0; i < takenAs.size(); i++) {
    if(i > 0 && takenAs[i] >= takenAs[i - 1]) {
      return 0;
    }
    ans += takenAs[i];
    if(i > 0 && takenWs[i] != takenWs[i - 1]) {
      ans -= c;
    }
  }
  return ans;
}

ll brute(ll n, ll c, vector<ll> ws, vector<ll> as) {
  reverse(all(ws));
  reverse(all(as));
  ll ans = 0;
  for(uint32_t mask = 0; mask < (1 << n); mask++) {
    ans = max(ans, getScore(n, c, ws, as, mask));
  }
  return ans;
}

ll solve(ll n, ll c, vector<ll> ws, vector<ll> as) {
  reverse(all(ws));
  reverse(all(as));
  auto nextSameW = getNextSameW(ws, as);
  auto nextSmaller = getNextSmaller(as);

  vector<ll> maxTaking(n);
  vector<ll> maxSuffix(n);

  maxSuffix.back() = maxTaking.back() = as.back();

  for(ll i = n - 1; i >= 0; i--) {
    maxTaking[i] = as[i];
    if(nextSameW[i] != -1) {
      maxTaking[i] = max(maxTaking[i], maxTaking[nextSameW[i]] + as[i]);
    }
    if(nextSmaller[i] != -1) {
      maxTaking[i] = max(maxTaking[i], as[i] + maxSuffix[nextSmaller[i]] - c);
    }
    maxSuffix[i] = maxTaking[i];
    if(i + 1 < n) {
      maxSuffix[i] = max(maxTaking[i], maxSuffix[i + 1]);
    }
  }

  return maxSuffix.front();
}

void solve() {
  ll n, c;
  cin >> n >> c;

  vector<ll> ws(n);
  vector<ll> as(n);

  for(ll i = 0; i < n; i++) {
    cin >> as[i] >> ws[i];
  }
  cout << solve(n, c, ws, as);
}

void test() {
  static mt19937 gen(123123);
  ll n = uniform_int_distribution<int>(1, 20)(gen);
  ll c = uniform_int_distribution<int>(1, 200)(gen);
  vector<ll> ws(n);
  vector<ll> as(n);  
  for(int i = 0; i < n; i++) {
    ws[i] = uniform_int_distribution<int>(1, 30)(gen);
    as[i] = uniform_int_distribution<int>(i == 0 ? 1 : as[i - 1], 50)(gen);
  }
  auto ans1 = solve(n, c, ws, as);
  auto ans2 = brute(n, c, ws, as);
  if(ans1 != ans2) {
    cout << "here we go" << endl;
    ans1 = solve(n, c, ws, as);
    ans2 = brute(n, c, ws, as);
    ans1 = solve(n, c, ws, as);
    ans2 = brute(n, c, ws, as);
    ans1 = solve(n, c, ws, as);
    ans2 = brute(n, c, ws, as);
    ans1 = solve(n, c, ws, as);
    ans2 = brute(n, c, ws, as);
  }
}

int main() {
  //for(int i = 0; i < 1000000; i++) {
  //  test();
  //}
  //return 0;
  //test();
  cin.tie(0)->sync_with_stdio(0);
  int t = 1;
  //cin >> t;
  while(t--) {
    solve();
    cout << "\n";
  }
  return 0;
}