#include <bits/stdc++.h>
using namespace std;
const int INF = 100000000;
int main(){
  int N, D;
  cin >> N >> D;
  vector<int> P(N), Q(N);
  for (int i = 0; i < N; i++){
    cin >> P[i] >> Q[i];
  }
  int tv = -INF, fv = 0;
  while (fv - tv > 1){
    int mid = (tv + fv) / 2;
    vector<vector<int>> dp(D, vector<int>(N, -INF));
    for (int i = 0; i < N; i++){
      if (-P[i] >= mid){
        dp[0][i] = -P[i] + Q[i];
      }
    }
    for (int i = 0; i < D - 1; i++){
      vector<int> L(N + 1);
      L[0] = -INF;
      for (int j = 0; j < N; j++){
        L[j + 1] = max(L[j], dp[i][j]);
      }
      vector<int> R(N + 1);
      R[N] = -INF;
      for (int j = N - 1; j >= 0; j--){
        R[j] = max(R[j + 1], dp[i][j]);
      }
      for (int j = 0; j < N; j++){
        int mx = max(L[j], R[j + 1]);
        if (mx - P[j] >= mid){
          dp[i + 1][j] = mx - P[j] + Q[j];
        }
      }
    }
    bool ok = false;
    for (int i = 0; i < N; i++){
      if (dp[D - 1][i] != -INF){
        ok = true;
      }
    }
    if (ok){
      tv = mid;
    } else {
      fv = mid;
    }
  }
  cout << tv << endl;
}