#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
#define rep(i,n) for(int i=0; i<(int)(n); i++)
#define rrep(i, n) for(int i=((int)(n)-1); i>=0; --i)
#define all(x) (x).begin(),(x).end()
#define MOD 1000000007
#define MOD2 998244353
#define INF 1000000007
#define LINF 1000000000000000007LL
#define PI 3.14159265359
#define P pair<ll,ll>
template <typename T>
inline bool chmax(T &a, const T &b){
  if(a<b) {a=b; return true;}
  else return false;
}
template <typename T>
inline bool chmin(T &a, const T &b){
  if(a>b) {a=b; return true;}
  else return false;
}
struct Edge{
  int to; ll cost;
  Edge(int to, ll cost) : to(to), cost(cost) {}
};
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
void add_edge(Graph &g,int from,int to,ll cost,bool rev,ll rev_cost){
  g[from].push_back(Edge(to,cost));
  if(rev) g[to].push_back(Edge(from,rev_cost));
}


struct fine{
  int p,q,d;
  fine(int p,int q, int d):p(p),q(q),d(d){}
};

void solve(){
  int n,d;
  cin>>n>>d;
  vector<fine> vec;
  rep(i,n){
    int p,q; cin>>p>>q;
    vec.push_back(fine(p,q,q-p));
  }
  
  auto comp = [](fine f1, fine f2){
    return f1.d>f2.d;
  };
  sort(all(vec),comp);

  int ok=-INF, ng=0;
  while(abs(ok-ng)>1){
    int mid = (ok+ng)/2;

    int pre=-1;   
    int val=0;

    bool f=1;
    rep(i,d){
      bool found=0;
      rep(j,n){
        if(val-vec[j].p >= mid && pre!=j){
          val += vec[j].d;
          pre=j;
          found=1;
          break;
        }
      }
      if(!found) f=0;
    }
    if(f) ok=mid;
    else ng=mid;
  }
  cout<<ok<<'\n';
}

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout<<setprecision(10)<<fixed;
  solve();
  return 0;
}