#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;

#define REP(i,n) for(int i=0;i<(n);i++)
#define RREP(i,n) for(int i=(n-1);i>=0;i--)
#define ALL(v) v.begin(),v.end()

const int INF=1e9+7;

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int n,d;cin>>n>>d;
  vector<int> p(n),q(n);
  REP(i,n)cin>>p[i]>>q[i];
  int ok=-INF,ng=INF;
  while(ng-ok>1){
    int mid=(ok+ng)>>1;
    vector<int> dp(n+1,-INF);
    dp[n]=0;
    REP(_,d){
      vector<int> mx(n+2),mx2(n+2);
      mx[0]=-INF;
      REP(i,n+1)mx[i+1]=max(mx[i],dp[i]);
      mx2.back()=-INF;
      for(int i=n;i>=0;i--)mx2[i]=max(mx2[i+1],dp[i]);
      vector<int> cpy(n+1,-INF);
      REP(i,n){
        int pre=max(mx[i],mx2[i+1]);
        if(pre-p[i]>=mid)cpy[i]=pre-p[i]+q[i];
      }
      dp=cpy;
    }
    bool fok=false;
    REP(i,n)if(dp[i]>-INF)fok=true;
    if(fok)ok=mid;
    else ng=mid;
  }
  cout<<ok<<endl;
}