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#include <bits/stdc++.h>

using namespace std;

#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) {}
#endif

#define int ll
#define x first
#define y second
#define ir(a, x, b) ((a) <= (x) && (x) <= (b))
#define vec vector
#define rep(i, a, b) for (int i = a; i < (b); ++i)
#define all(x) (x).begin(), (x).end()

using ll = long long;


using pii = pair<int, int>;

#define cm(a, b) a = max((a), (b))

signed main() {
    cin.tie(0)->sync_with_stdio(0);
    int N, C;
    cin >> N >> C;
    vec<ll> a(N);
    vec<ll> w(N);
    rep (n, 0, N) {
        cin >> a[n] >> w[n];
        --w[n];
    }
    int i = 0;
    ll K = 500001;
    vec<ll> dp(K);
    multiset<ll> vs;
    while (i < N) {
        vec<pii> changes;
        int j;
        for (j = i; j < N && a[i] == a[j]; j++) {
            debug(j);
            ll v = dp[w[j]];
            cm(v, a[j] + dp[w[j]]);

            if (vs.size()) {
                auto it = vs.rbegin();
                bool b = true;
                if (*it == dp[w[j]]) {
                    it++;
                    if (it == vs.rend()) b = false;
                }
                if (b)
                    cm(v, a[j] - C + *it);
            }
            changes.push_back({w[j], v});
        }
        for (auto [a, b] : changes) {
            debug(a, b);
            auto it = vs.find(dp[a]);
            if (it != vs.end())
                vs.erase(it);
            dp[a] = b;
            vs.insert(b);
        }
        i = j;
    }
    cout << *vs.rbegin() << "\n";
    return 0;
}