#include <bits/stdc++.h>
using namespace std;

long long int patternTops[500'001] = { 0 };

void reduceBlocks(vector<pair<long long int, int>> &blocks,
		vector<pair<long long int, int>> &reducedBlocks) {
	const int S = blocks.size();
	reducedBlocks.push_back(blocks[0]);
	for (int i = 1; i < S; i++) {
		if (blocks[i].second == blocks[i - 1].second) {
			reducedBlocks.back().first += blocks[i].first;
		} else {
			reducedBlocks.push_back(blocks[i]);
		}
	}
}

void resolve2(vector<pair<long long int, int>> blocks, int n, int c) {
	vector<pair<long long int, int>> reducedBlocks;
	reduceBlocks(blocks, reducedBlocks);


	const int RS = reducedBlocks.size();



	pair<long long int, int> p;
	long long int lastFitting, newTop1, newTop2;
	long long int top = 0;
	for (int i = RS - 1; i >= 0; i--) {
		p = reducedBlocks[i];
		lastFitting = patternTops[p.second];
		newTop1 = top + p.first - c;
		newTop2 = lastFitting + p.first;
		patternTops[p.second] = max(newTop1, newTop2);
		top = max(top, patternTops[p.second]);
	}

	cout << top << endl;

}

int main() {

	cin.tie(NULL);
	cout.tie(NULL);
	ios_base::sync_with_stdio(false);

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

	vector<pair<long long int, int>> blocks(n);

	for (int i = 0; i < n; i++) {
		cin >> blocks[i].first;
		cin >> blocks[i].second;
	}

	resolve2(blocks, n, c);

	return 0;
}