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
#include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define all(x) begin(x), end(x)
#define sz(x) int((x).size())
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;

#ifdef LOCAL
auto operator<<(auto& o, auto x) -> decltype(x.first, o);
auto operator<<(auto& o, auto x) -> decltype(x.end(), o) {
  o << "{";
  for (int i = 0; auto y : x) o << ", " + !i++ * 2 << y;
  return o << "}"; }
auto operator<<(auto& o, auto x) -> decltype(x.first, o) {
  return o << "(" << x.first << ", " << x.second << ")"; }
void __print(auto... x) { ((cerr << x << " "), ...) << endl; }
#define debug(x...) __print("[" #x "]:", x)
#else
#define debug(...) 2137
#endif

const int nax = 5e5 + 10;

struct DS {
  int n, c;
  vector<ll> v;
  pair<ll, int> mx1, mx2;
  DS(int n, int c) : n(n), c(c) {
    v.resize(n);
  }
  ll get(int i, ll x) {
    ll val = v[i] + x;
    if(mx1.second != i) {
      val = max(val, mx1.first + x - c);
    } else {
      val = max(val, mx2.first + x - c);
    }
    return val;
  }
  void upd(int i, ll x) {
    if(x < v[i]) return;
//    debug(i, x);
    v[i] = x;
    if(x >= mx1.first) {
      if(mx1.second != i) mx2 = mx1;
      mx1 = {x, i};
    } else if(x >= mx2.first) {
      mx2 = {x, i};
    }
  }
};

int main() {
  cin.tie(0)->sync_with_stdio(0);

  int n, c;
  cin >> n >> c;
  DS d(nax, c);
  vector<int> a(n), w(n);
  for(int i = 0; i < n; i++) cin >> a[i] >> w[i];
  for(int i = 0, j = 0; i < n; i = j) {
    while(j < n && a[i] == a[j]) j++;
    vector<pair<int, ll>> v;
    v.reserve(j - i);
    for(int k = i; k < j; k++) {
      v.push_back({w[k], d.get(w[k], a[k])});
    }
    for(auto [ww, val] : v) {
      d.upd(ww, val);
    }
  }
  cout << d.mx1.first << endl;
}