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
78
79
80
#include <bits/stdc++.h>
using namespace std;

#define mp make_pair
#define pb push_back
#define st first
#define nd second
#define fi first
#define se second
#define vt vector
#define FOR(a, b, c)  for(int a=b; a<c; ++a)
#define all(a)     (a).begin(),(a).end()
#define sz(a)      (int)(a).size()

typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
typedef vector<int> vi; 
typedef vector<ll> vll;
typedef pii PII;
typedef pll PLL;

constexpr ll nax = 5e5+6969, INF = 1e9+2137;
constexpr ld eps = 1e-9;

mt19937_64 rng(6969);
// mt19937_64 rng(chrono::system_clock::now().time_since_epoch().count());

inline ll rand(ll l, ll r) {
	return uniform_int_distribution<ll>(l, r)(rng);
}

int n, c; 
ll smaller[nax], same[nax], color[nax], pref[nax], dp[nax]; 

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

    cin >> n >> c; 
    vector<pll> v(n); 
    for(auto &e: v) {
        int a, b; 
        cin >> a >> b; 
        e = mp(a, b); 
    }

    color[v[0].se] = 1; 
    for(int i = 2; i <= n; i++) {
        int h = v[i-1].fi, w = v[i-1].se; 
        if(h > v[i-2].fi) {
            smaller[i] = i-1; 
        }
        else {
            smaller[i] = smaller[i-1]; 
        }

        same[i] = color[w]; 

        if(same[i] > 0 && v[same[i]-1].fi == h) {
            same[i] = same[same[i]]; 
        }

        color[w] = i; 
    }

    // for(int i = 1; i <= n; i++) {
    //     cout << smaller[i] << " " << same[i] << "\n"; 
    // }

    for(int i = 1; i <= n; i++) {
        int h = v[i-1].fi, w = v[i-1].se; 
        dp[i] = max(dp[same[i]] + h, pref[smaller[i]] + h - c); 
        pref[i] = max(pref[i-1], dp[i]); 
    }

    cout << pref[n] << "\n"; 
    
    return 0;
}