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// clang-format off
#include <bits/stdc++.h>

using namespace std;

#define ALL(x) (x).begin(), (x).end()

template<class C> void mini(C &a5, C b5) { a5 = min(a5, b5); }
template<class C> void maxi(C &a5, C b5) { a5 = max(a5, b5); }

#ifdef LOCAL
const bool debug = true;
#else
const bool debug = false;
#define cerr if (true) {} else cout
#endif
// clang-format on

#define int long long
#define double long double

const int INF = 1e18;
const int mod = 1e9 + 7;
const int nax = 1e6;

// size, result
pair<int, int> best[nax], current, previous;

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

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

    for (int i = 0; i < n; i++) {
        int a, w;
        cin >> a >> w;

        if (current.first != a) {
            previous = current;
            current.first = a;
        }

        if (a != best[w].first)
            best[w] = {a, best[w].second + a};
        maxi(best[w].second, previous.second + a - c);

        maxi(current.second, best[w].second);
    }

    cout << current.second;
    
    return 0;
}/*

*/