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#include <algorithm>
#include <cstdint>
#include <cstdio>
#include <ranges>
#include <vector>

struct Brick {
  Brick(const int& size_, const int& color_) : size(size_), color(color_) {}
  bool operator<(const Brick& brick) const { return color < brick.color; }
  bool operator==(const Brick& brick) const { return color == brick.color; }

  int size;
  int color;
};

struct Tower {
  Tower() : size(0), color(0), score(0) {}
  Tower(const int& size_, const int& color_, const int64_t& score_) : size(size_), color(color_), score(score_) {}
  void addBrick(const Brick& brick, const int& c) {
    size = brick.size;
    score += size;
    if (brick.color != color) {
      score -= c;
    }
  }

  int size;
  int color;
  int64_t score;
};

using Bricks = std::vector<Brick>;
using Towers = std::vector<Tower>;

void process(Towers& towers, Tower& bestTower, const Bricks& bricks, const int& c) {
  Tower newBestTower = bestTower;
  for (const auto& brick : bricks) {
    if (0 == towers[brick.color].score) {
      if (brick.size < bestTower.score + brick.size - c) {
        towers[brick.color] = {brick.size, brick.color, bestTower.score + brick.size - c};
      } else {
        towers[brick.color] = {brick.size, brick.color, brick.size};
      }
    } else {
      if (towers[brick.color].score + brick.size < bestTower.score + brick.size - c) {
        towers[brick.color].score = bestTower.score + brick.size - c;
        towers[brick.color].size = brick.size;
      } else {
        towers[brick.color].addBrick(brick, c);
      }
    }
    if (newBestTower.score < towers[brick.color].score) {
      newBestTower = towers[brick.color];
    }
  }
  bestTower = newBestTower;
}

int main() {
  int n, c;
  int size, color;
  std::vector<Bricks> sortedBricks;

  int lastSize = 0;
  int maxColor = 0;
  scanf("%d %d\n", &n, &c);
  for (int i = 0; i < n; ++i) {
    scanf("%d %d\n", &size, &color);
    if (size != lastSize) {
      sortedBricks.push_back({});
    }
    sortedBricks.back().emplace_back(size, color);
    lastSize = size;
    maxColor = std::max(maxColor, color);
  }
  for (auto& bricks : sortedBricks) {
    std::sort(bricks.begin(), bricks.end());
    bricks.erase(std::unique(bricks.begin(), bricks.end()), bricks.end());
  }
  Towers towers;
  towers.resize(maxColor + 1);
  for (int i = 1; i <= maxColor; ++i) {
    towers[i].color = i;
  }
  Tower bestTower(0, 0, 0);
  for (const auto& brick : sortedBricks.front()) {
    towers[brick.color].addBrick(brick, c);
    bestTower = towers[brick.color];
  }
  for (const auto& bricks : sortedBricks | std::views::drop(1)) {
    process(towers, bestTower, bricks, c);
  }
  printf("%ld\n", bestTower.score);
  return 0;
}