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#include <bits/stdc++.h>

using namespace std;

typedef long long ll;


int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);

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

    int max_pattern = 1;

    vector<pair<int, int>> v;
    for (int i = 1; i <= n; i++) {
        pair<int, int> p;
        cin >> p.first >> p.second;
        max_pattern = max(max_pattern, p.second);
        v.push_back(p);
    }
    sort(v.begin(), v.end());

    vector<pair<int, int>> bricks;
    for (int i = 0; i < v.size(); i++) {
        if (!(i > 0 && v[i].first == v[i - 1].first && v[i].second == v[i - 1].second)) {
            bricks.push_back(v[i]);
        }
    }

    vector<int> partition_indices;
    partition_indices.push_back(0);
    for (int i = 1; i < bricks.size(); i++) {
        if (bricks[i].first != bricks[i - 1].first) {
            partition_indices.push_back(i);
        }
    }
    partition_indices.push_back(bricks.size());

    set<ll> res;
    set<ll> res_pattern[max_pattern + 1];

    for (int k = 0; k < partition_indices.size() - 1; k++) {
        vector<pair<ll, int>> results;

        for (int ind = partition_indices[k]; ind < partition_indices[k + 1]; ind++) {
            ll result = bricks[ind].first;
            if (!res_pattern[bricks[ind].second].empty()) {
                result += *prev(res_pattern[bricks[ind].second].end());
            }
            if (!res.empty()) {
                result = max(result, bricks[ind].first - c + *prev(res.end()));
            }
            pair<ll, int> q;
            q.first = result;
            q.second = bricks[ind].second;
            results.push_back(q);
        }

        for (int i = 0; i < results.size(); i++) {
            auto q = results[i];
            res_pattern[q.second].insert(q.first);
            res.insert(q.first);
        }
    }

    cout << *(prev(res.end())) << "\n";

    return 0;
}