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#include <iostream>
#include <vector>

using namespace std;

#define MAXW 500001
#define LL long long
#define NEG (-1000000000000000000LL)

struct Block {
    int a, w;
};

class Solver {
public:
    static void solve() {
        int n, c;
        vector<Block> blocks;

        cin >> n >> c;

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

        vector<LL> bestForPattern(MAXW, NEG);
        LL best_global = NEG;
        LL second_best_global = NEG;
        int best_global_pattern = -1;
        LL ans = 0;
        int i = 0;
        while (i < n) {
            int currA = blocks[i].a;
            vector<pair<int, LL> > group;
            while (i < n && blocks[i].a == currA) {
                int w = blocks[i].w;
                LL cand1 = bestForPattern[w];

                LL cand2;
                if (best_global_pattern == w)
                    cand2 = second_best_global;
                else
                    cand2 = best_global;
                LL cand2_adj = (cand2 == NEG ? NEG : cand2 - c);

                LL bestPrev = max(cand1, cand2_adj);
                bestPrev = max(bestPrev, 0LL);
                LL dp = currA + bestPrev;
                group.emplace_back(w, dp);
                ans = max(ans, dp);
                i++;
            }

            for (auto &[fst, snd]: group) {
                const int w = fst;
                LL dp = snd;
                bestForPattern[w] = max(bestForPattern[w], dp);
                if (dp > best_global) {
                    if (best_global_pattern == w) {
                        best_global = dp;
                    } else {
                        second_best_global = best_global;
                        best_global = dp;
                        best_global_pattern = w;
                    }
                } else if (w != best_global_pattern && dp > second_best_global) {
                    second_best_global = dp;
                }
            }
        }
        cout << ans << endl;
    }
};

int main() {
    Solver::solve();
    return 0;
}