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#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
const int MAXN=5e5;

ll val[MAXN+5];
int typ[MAXN+5];
ll od[MAXN+5];

void solve()
{
	int n;
	ll c;
	cin >> n >> c;
	for(int i=0;i<n;i++){
		cin >> val[i] >> typ[i];
	}
	ll best=0;
	vector<pair<ll,int>> to_update;
	for(int i=n-1;i>=0;i--){
		if(val[i]!=val[i+1]){
			for(pair<ll,int> pr : to_update){
				best=max(best,pr.first);
				od[pr.second]=max(od[pr.second], pr.first);
			}
			to_update.clear();
		}
		ll res;
		res=max(best-c+val[i], od[typ[i]]+val[i]);
		//cout << res << " ";
		to_update.push_back({res,typ[i]});
	}
	for(pair<ll,int> pr : to_update){
		best=max(best,pr.first);
	}
	cout << best;
}

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	solve();
	
	return 0;
}