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

#define int long long
#define ii pair<int,int>
#define iii tuple<int,int,int>
#define fi first
#define se second
#define endl '\n'

#define pub push_back
#define pob pop_back
#define puf push_front
#define pof pop_front
#define lb lower_bound
#define ub upper_bound

#define rep(x,start,end) for(int x=(start)-((start)>(end));x!=(end)-((start)>(end));((start)<(end)?x++:x--))
#define all(x) (x).begin(),(x).end()
#define sz(x) (int)(x).size()

mt19937 rng(chrono::system_clock::now().time_since_epoch().count());

int n,k;
ii arr[500005];
int dp[500005];

signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin.exceptions(ios::badbit | ios::failbit);
	
	cin>>n>>k;
	rep(x,1,n+1) cin>>arr[x].fi>>arr[x].se;
	
	int MX=0;
	
	int l=1;
	while (l<=n){
		vector<ii> tmp;
		
		do{
			int val=arr[l].fi+max(dp[arr[l].se],MX-k);
			tmp.pub({val,arr[l].se});
			l++;
		} while (l<=n && arr[l-1].fi==arr[l].fi);
		
		for (auto [a,b]:tmp){
			dp[b]=max(dp[b],a);
			MX=max(MX,a);
		}
	}
	
	cout<<MX<<endl;
}