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
#include <bits/stdc++.h>
/*#pragma GCC target ("avx2,fma")
#pragma GCC optimize ("Ofast")
#pragma GCC optimize ("unroll-loops")*/

#define int long long
#define ll long long
#define ld long double
#define endl '\n'
#define st first
#define nd second
#define pb push_back
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define FOR(i,l,r) for(int i=(l);i<=(r);i++)
#define ROF(i,r,l) for(int i=(r);i>=(l);i--)
using namespace std;
ll infl=1000000000000000007;
int inf=1000000007;
int mod=998244353;
int mod1=998244353;

#ifdef DEBUG
auto&operator<<(auto&o,pair<auto,auto>p){return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator<<(auto&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<","+!i++<<e;return o<<"}";}
#define debug(X...)cerr<<"["#X"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(X)
#else
#define debug(...){}
#endif

const int N=500007;

int DP[N];
int MX[N];

signed main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
	int n,c;
	cin>>n>>c;
	vector<pair<int,int>>a(n);
	FOR(i,0,n-1) cin>>a[i].st>>a[i].nd;
	sort(all(a));
	int ans=0,j=-1,mx=0;
	FOR(i,0,n-1)
	{
		while(a[j+1].st<a[i].st) 
		{
			j++;
			mx=max(mx,DP[j]);
			MX[a[j].nd]=max(MX[a[j].nd],DP[j]);
		}
		DP[i]=a[i].st+MX[a[i].nd];
		DP[i]=max(DP[i],a[i].st+mx-c);
		ans=max(ans,DP[i]);
	}
	cout<<ans<<endl;
    
    
    
    
    
    
    return 0;
}