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#include <vector>
#include <cstdio>
#include <stack>
#include <algorithm>
#include <queue>
#include <map>
#include <cmath>
#include <unordered_set>
#include <unordered_map>
#include <set>
#include <cstring>
#include <bitset>
#include <iostream>
#include <queue>
#include <iomanip>
#include <complex>

using namespace std;

#define ALL(x) x.begin(), x.end()
#define UNIQUE(c) (c).resize(unique(ALL(c)) - (c).begin())
#define FOR(i, a, b) for(int i =(a); i <=(b); ++i)
#define RE(i, n) FOR(i, 1, n)
#define RED(i, n) FORD(i, n, 1)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define REP(i, n) for(int i = 0;i <(n); ++i)
#define REPD(i, n) FORD(i, n-1,0)

#define printA(a, L, R) FOR(i,L,R) cout << a[i] << (i==R?'\n':' ')
#define printV(a) printA(a,0,a.size()-1)
#define PRESENT(c, x) ((c).find(x) != (c).end())
#define CPRESENT(c, x) (find(ALL(c),x) != (c).end())
#define bit(x, i) (x&(1<<i))
#define lowbit(x) ((x)&((x)^((x)-1)))

const int fx[4][2] = {{0,  1},
                      {0,  -1},
                      {1,  0},
                      {-1, 0}};
const int fxx[8][2] = {{0,  1},
                       {0,  -1},
                       {1,  0},
                       {-1, 0},
                       {1,  1},
                       {1,  -1},
                       {-1, 1},
                       {-1, -1}};
const int sk[8][2] = {{2,  1},
                      {2,  -1},
                      {-2, -1},
                      {-2, 1},
                      {1,  2},
                      {-1, 2},
                      {1,  -2},
                      {-1, -2}};

const int maxn = 1000012;
long long mod = 998244353ll;
const long long inf = 10000000000012ll;

long long  n, c;
pair<long long, int>a[maxn], res1, res2;
set<pair<long long, int> > st;
long long naj[maxn];
void solve() {
    cin>>n>>c;
    REP(i, n) cin>>a[i].first>>a[i].second;

    sort(a, a+n);
    st.emplace(0, 0);
    REP(i, n) {
        if (i > 0 && a[i].first == a[i-1].first && a[i].second == a[i-1].second) {
            if (a[i + 1].first != a[i].first) {
                res1 = *st.rbegin();
                res2 = *next(st.rbegin());
            }
            continue;
        }
        long long res = naj[a[i].second] + a[i].first;
        if (res1.second != a[i].second) {
            res = max(res, res1.first + a[i].first - c);
        } else {
            res = max(res, res2.first + a[i].first - c);
        }
        st.erase({naj[a[i].second], a[i].second});
        naj[a[i].second] = max(res, naj[a[i].second]);
        st.insert({naj[a[i].second], a[i].second});

        if (a[i + 1].first != a[i].first) {
            res1 = *st.rbegin();
            res2 = *next(st.rbegin());
        }
    }
    cout<<st.rbegin()->first<<"\n";
}

int main() {
    ios_base::sync_with_stdio(false), cin.tie(nullptr);

    int tt = 1;
//    cin >> tt;`
    while (tt--) {
        solve();
    }
    return 0;
}