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#include <bits/stdc++.h>

using std::cin, std::cout;
using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
const char endl = '\n';

const int MAX_N = 500005;

struct box {
    i64 height, pattern;
};

int prev_with_pattern[MAX_N]{};
int next_same[MAX_N]{};
box boxes[MAX_N];
i64 best_pen[MAX_N]{};
i64 best_no_pen[MAX_N]{};
int next_larger[MAX_N]{};

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

    int n, penalty;    
    cin >> n >> penalty;

    std::ranges::fill(prev_with_pattern, -1);
    std::ranges::fill(next_same, -1);

    for (int i = 0; i < n; i++) {
        int height, pattern;
        cin >> height >> pattern;

        boxes[i] = {height, pattern};

        if (prev_with_pattern[pattern] != -1) {
            if (boxes[prev_with_pattern[pattern]].height == height) continue; // we cant take it anyways
            next_same[prev_with_pattern[pattern]] = i;
        }
        prev_with_pattern[pattern] = i;
    }

    {
        int prev_i = n;
        int prev = boxes[n - 1].height;

        for (int i = n - 1; i >= 0; i--) {
            if (boxes[i].height < prev) {
                prev_i = i + 1;
            }

            next_larger[i] = prev_i;

            prev = boxes[i].height;
        }
    }

    for (int i = 0; i < n; i++) {
        i64 next_score = std::max(best_pen[i] + boxes[i].height - penalty, best_no_pen[i] + boxes[i].height);
        if (next_same[i] != -1) {
            if (next_score > best_no_pen[next_same[i]]) best_no_pen[next_same[i]] = next_score;
        }
        if (next_score > best_pen[next_larger[i]]) best_pen[next_larger[i]] = next_score;
        if (best_pen[i] > best_pen[i + 1]) best_pen[i + 1] = best_pen[i];
    }

    cout << std::max(best_pen[n], best_no_pen[n]);

    return 0;
}