#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

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

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

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

    vector<long long> dp(n);
    long long max_score = 0;

    for (int i = 0; i < n; ++i) {
        dp[i] = blocks[i].first;  // Wysokość wieży z jednym klockiem
        for (int j = 0; j < i; ++j) {
            if (blocks[j].first < blocks[i].first) {
                long long score = dp[j] + blocks[i].first;
                if (blocks[j].second != blocks[i].second) {
                    score -= c;
                }
                if (score > dp[i]) {
                    dp[i] = score;
                }
            }
        }
        if (dp[i] > max_score) {
            max_score = dp[i];
        }
    }

    cout << max_score << endl;

    return 0;
}