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#include <bits/stdc++.h>

using namespace std;

#define ll long long

#define rng(i,a,b) for(int i=int(a);i<int(b);i++)
#define rep(i,b) rng(i,0,b)

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;

typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;

typedef pair<int,int> ii;

template<class t> using vc=vector<t>;
template<class t> using vvc=vc<vc<t>>;

const int MOD = 998244353;

ll read(){
    ll i;
    cin>>i;
    return i;
}

vi readvi(int n,int off=0,int shift=0){
    vi v(n+shift);
    rep(i,shift)v[i]=0;
    rep(i,n)v[i+shift]=read()+off;
    return v;
}

void YesNo(bool condition, bool do_exit=true) {
    if (condition)
        cout << "Yes" << endl;
    else
        cout << "No" << endl;
    if (do_exit)
        exit(0);
}

int main(void ) {
    ios::sync_with_stdio(false);
    cin.tie(NULL);

    set<ii> s;

    int n, c;
    cin >> n >> c;
    vi a;
    vi w;
    rep(i,n) {
      int aa, ww;
      cin >> aa >> ww;
      if (s.count({aa,ww}) == 0) {
          a.push_back(aa);
          w.push_back(ww);
          s.insert({aa,ww});
      }
    }
    n = a.size();

    std::reverse(a.begin(), a.end());
    std::reverse(w.begin(), w.end());

    const int MAX_COL = 500000;

    vl dp(MAX_COL+1, 0);

    ll best = 0;
    ll new_best = 0;

    int i = 0;
    while (i < n) {
        int size = a[i];
        while (i < n and a[i] == size) {
            dp[w[i]] = max(a[i] + dp[w[i]], a[i] + best - c);
            new_best = max(new_best, dp[w[i]]);
            ++i;
        }
        best = new_best;
    }

    cout << best << endl;;

    return 0;
}