#pragma GCC optimize("O3")
#pragma GCC target ("avx2")
#include<bits/stdc++.h> 
using namespace std;
using ll=long long;
using P=pair<ll,ll>;
template<class T> using V=vector<T>; 
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
const ll inf=(1e18);
//const ll mod=998244353;
const ll mod=1000000007;
ll GCD(ll a,ll b) {return b ? GCD(b,a%b):a;}
ll LCM(ll c,ll d){return c/GCD(c,d)*d;}
struct __INIT{__INIT(){cin.tie(0);ios::sync_with_stdio(false);cout<<fixed<<setprecision(20);}} __init;
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T>void debag(const vector<T> &a){cerr<<"debag :";for(auto v:a)cerr<<v<<" ";cerr<<"\n";}
template<class T>void print(const vector<T> &a){for(auto v:a)cout<<v<<" ";cout<<"\n";}
int main(){
      ll n,d;
      cin>>n>>d;
      ll l=-(1e10),r=(1e10);
      V<ll> p(n),q(n);
      for(int i=0;i<n;i++)cin>>p[i]>>q[i];
      while(r-l>1){
            ll a=0,ab=-1,b=-inf,bb=-1;
            ll mid=(l+r)/2;
            for(int i=0;i<d;i++){
                  ll na=-inf,nb=-inf,nab=-1,nbb=-1,nc=-inf,ncb=-1;
                  for(int j=0;j<n;j++){
                        if(a-p[j]>=mid&&ab!=j){
                              if(na<a-p[j]+q[j]){
                                    nc=nb;
                                    ncb=nbb;
                                    nb=na;
                                    nbb=nab;
                                    nab=j;
                                    na=a-p[j]+q[j];
                              }else if(nb<a-p[j]+q[j]){
                                    nc=nb;
                                    ncb=nbb;
                                    nbb=j;   
                                    nb=a-p[j]+q[j];                       
                              }else if(nc<a-p[j]+q[j]){
                                    ncb=j;
                                    nc=a-p[j]+q[j];
                              }
                        }
                        if(b-p[j]>=mid&&bb!=j){
                              if(na<b-p[j]+q[j]){
                                    nc=nb;
                                    ncb=nbb;
                                    nb=na;
                                    nbb=nab;
                                    nab=j;
                                    na=b-p[j]+q[j];
                              }else if(nb<b-p[j]+q[j]){
                                    nc=nb;
                                    ncb=nbb;
                                    nbb=j;   
                                    nb=b-p[j]+q[j];                       
                              }else if(nc<b-p[j]+q[j]){
                                    ncb=j;
                                    nc=b-p[j]+q[j];
                              }
                        }
                  }
                  a=na;ab=nab;
                  if(nab==nbb){
                        b=nc;
                        bb=ncb;
                  }else{
                        b=nb;
                        bb=nbb;
                  }
            }
            if(a>=mid)l=mid;
            else r=mid;
      }
      cout<<l<<"\n";
}