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

#define int long long

inline int MAX(int a, int b) {return (a > b) ? a : b;}

int bin(vector<pair<int, int>> a, int x) {
    int l = 0, r = a.size();
    while (l < r) {
        int m = (l + r) / 2;
        if (a[m].first <= x) {
            r = m;
        } else {
            l = m + 1;
        }
    }
    return l;
}

int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0);

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

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

    unordered_map<int, vector<pair<int, int>>> mp;
    vector<pair<int, int>> dp;

    int ans = 0;

    for (auto &it : v) {
        int a = it.first;
        int w = it.second;
        int cur = a;
        auto &l = mp[w];
        
        int samew = 0;
        if (!l.empty()) {
            int x = bin(l, a);
            if (x > 0) {
                samew = l[x - 1].second;
            }
        }

        int diffw = 0;
        int gx = bin(dp, a);
        if (gx > 0) {
            diffw = dp[gx - 1].second;
        }
        int diff = MAX(diffw - c, 0);

        cur += MAX(samew, diff);
        ans = MAX(ans, cur);
        
        if (l.empty() || a < l.back().first) {
            int neoans = cur;
            if (!l.empty()) {
                neoans = MAX(neoans, l.back().second);
                l.pop_back();
            }
            l.push_back({a, neoans});
        } else {
            l.back().second = MAX(l.back().second, cur);
        }

        if (dp.empty() || a < dp.back().first) {
            int ngx = cur;
            if (!dp.empty()) {
                ngx = MAX(ngx, dp.back().second);
                dp.pop_back();
            }
            dp.push_back({a, ngx});
        } else {
            dp.back().second = MAX(dp.back().second, cur);
        }
    }

    cout << ans;
}