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

int main() {
    ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int n, c;
    cin >> n >> c;
    vector<pair<int, int>> v(n+1);
    vector<int> dp(n+1, 0);
    
    for (int i = 1; i <= n; i++) {
        cin >> v[i].first >> v[i].second;
    }
    
    sort(v.begin() + 1, v.end(), greater());
    
    for (int i = 1; i <= n; i++) {
        dp[i] = v[i].first;
    }

    for (int i = 1; i <= n; i++) {
        for (int j = i + 1; j <= n; j++) {
            if (v[j].first < v[i].first) {
                int z = (v[i].second == v[j].second) ? 0 : c;
                dp[j] = max(dp[j], dp[i] + v[j].first - z);
            }
        }
    }

    cout << *max_element(dp.begin(), dp.end());
}