#include<iostream>
#include<set>
#include<vector>
#include<algorithm>
using namespace std;
int N,D;
main()
{
	cin>>N>>D;
	vector<pair<int,pair<int,int> > >PQ(N);
	for(int i=0;i<N;i++)
	{
		int p,q;cin>>p>>q;
		PQ[i]=make_pair(p,make_pair(p-q,i));
	}
	sort(PQ.begin(),PQ.end());
	int L=-1e9,R=1;
	while(R-L>1)
	{
		int mid=(L+R)/2;
		bool ok[2]={true,true};
		int now[2]={0,0},id[2]={0,0};
		multiset<pair<int,int> >S[2];
		int prv[2]={-1,-1};
		for(int d=0;d<D;d++)
		{
			for(int i=0;i<2;i++)if(ok[i])
			{
				while(id[i]<N&&PQ[id[i]].first<=now[i]-mid)
				{
					S[i].insert(PQ[id[i]++].second);
				}
				while(id[i]>0&&PQ[id[i]-1].first>now[i]-mid)
				{
					S[i].erase(S[i].find(PQ[--id[i]].second));
				}
			}
			if(d==0)
			{
				auto it=S[0].begin();
				if(it==S[0].end())
				{
					ok[0]=ok[1]=false;
				}
				else
				{
					now[0]-=it->first;
					prv[0]=it->second;
					it++;
					if(it==S[0].end())
					{
						ok[1]=false;
					}
					else
					{
						now[1]-=it->first;
						prv[1]=it->second;
					}
				}
			}
			else
			{
				for(int i=0;i<2;i++)if(ok[i])
				{
					if(S[i].empty())
					{
						ok[i]=false;
						continue;
					}
					auto it=S[i].begin();
					if(it->second!=prv[i])
					{
						now[i]-=it->first;
						prv[i]=it->second;
					}
					else
					{
						it++;
						if(it!=S[i].end())
						{
							now[i]-=it->first;
							prv[i]=it->second;
						}
						else ok[i]=false;
					}
				}
			}
		}
		if(ok[0]||ok[1])L=mid;
		else R=mid;
	}
	cout<<L<<endl;
}