1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
// Witold Milewski
// PA 2025
#include <bits/stdc++.h>
#define int long long
#define i128 __int128_t
using namespace std;
#define FOR(i, a, b) for(int i=a; i<=b; ++i)
#define FORB(i, b, a) for(int i=b; i>=a; --i)
#define sz(A) (int)(A.size())
#define ll long long
#define eb emplace_back
#define pb push_back
#define pi pair<int, int>
#define f first
#define s second
#define rs resize
#define V vector

V<V<pi>> kub;
const int base=(1<<19);

struct SegTree {
  int T[2*base];
  void update(int v, int x) {
    v+=base;
    T[v]=max(T[v], x);
    v/=2;
    while(v>=1) {
      T[v]=max(T[2*v], T[2*v+1]);
      v/=2;
    }
  }
  int query(int a, int b) {
    a+=base-1;
    b+=base+1;
    int res=0;
    while(a/2 != b/2) {
      if(a%2==0) res=max(res, T[a+1]);
      if(b%2==1) res=max(res, T[b-1]);
      a/=2; b/=2;
    }
    return res;
  }
} AT;

int n, c;

signed main() {
  cin.tie(0) -> ios_base::sync_with_stdio(0);
  cin >> n >> c;
  kub.rs(500007);
  V<pi> A;
  int a, w;
  FOR(i, 1, n) {
    cin >> a >> w;
    A.pb({a, w});
  }
  reverse(A.begin(), A.end());

  for(auto &[a, w] : A) {
    kub[a].pb({a, w});
  }

  int WYN=0;
  FORB(aa, 500000, 0) {
    V<pi> odp;
    for(auto &[a, w] : kub[aa]) {
      int wyn = a+max(AT.query(w, w), max(AT.query(1, w-1), AT.query(w+1, base-1))-c);
      odp.pb({w, wyn});
    }
    for(auto &[gdzie, wyn] : odp) {
      AT.update(gdzie, wyn);
    }
    WYN=max(WYN, AT.T[1]);
  }
  cout << WYN << '\n';
}