#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000

pair<long long,int> op(pair<long long,int> a,pair<long long,int> b){
	return max(a,b);
}

pair<long long,int> e(){
	return make_pair(-Inf,-1);
}

int main(){
	
	int N,D;
	cin>>N>>D;
	
	vector<int> p(N),q(N);
	rep(i,N)cin>>p[i]>>q[i];
	vector<pair<long long,long long>> ps;
	rep(i,N){
		q[i] = q[i] - p[i];
		p[i] *= -1;
		ps.emplace_back(p[i],q[i]);
	}
	sort(ps.begin(),ps.end());
	vector<pair<long long,int>> t(ps.size());
	rep(i,ps.size()){
		t[i] = make_pair(ps[i].second,i);
	}
	long long ok = Inf,ng = 0LL;
	while(ok-ng>1LL){
		long long mid = (ok+ng)/2;
		
		long long cur = 0LL;
		segtree<pair<long long,int>,op,e> seg(t);
		bool f = true;
		int last = -1;
		rep(_,D){
			pair<long long,long long> temp = make_pair(-mid - cur, -1);
			int d = lower_bound(ps.begin(),ps.end(),temp) - ps.begin();//distance(ps.begin,lower_bound(ps.begin(),ps.end(),temp));
			
			auto ret = seg.prod(d,t.size());
			if(ret.second==-1){
				f = false;
				break;
			}
			
			cur += ret.first;
			
			if(last!=-1){
				seg.set(last,make_pair(ps[last].second,last));
			}
			last = ret.second;
			seg.set(last,e());
			
		}
		if(f)ok = mid;
		else ng = mid;
	}
	
	cout<<-ok<<endl;
	
	
	return 0;
}