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#include<set>
#include<map>
#include<queue>
#include<vector>
#include<algorithm>
#include<bits/stdc++.h>
#define pr pair
#define f first
#define s second
#define ll long long
#define mp make_pair
#define pll pr<ll,ll>
#define pii pr<int,int>
#define piii pr<int,pii>
using namespace std;
ll mx[500005];
int a[500005],v[500005];
ll dp[500005];
int main()
{
	ios_base::sync_with_stdio(0);
	int n,c;
	ll cx=c;
	cin>>n>>c;
	for(int i=0;i<n;i++) cin>>a[i]>>v[i];
	ll ans=0;
	for(int i=0;i<n;)
	{
		int j=i;
		for(;j<n;j++) if(a[j]!=a[i]) break;
		for(int k=i;k<j;k++)
		{
			dp[k]=max(cx-c,mx[v[k]])+a[k];
		}
		for(int k=i;k<j;k++)
		{
			cx=max(cx,dp[k]);
			mx[v[k]]=max(mx[v[k]],dp[k]);
			ans=max(ans,dp[k]);
		}
		i=j;
	}
	cout<<ans<<endl;
	return 0;
}