#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <vector>
using namespace std;
using ll = long long;
#define rep(i, j, n) for (int i = j; i < (n); ++i)
#define rrep(i, j, n) for (int i = (n)-1; j <= i; --i)
#define all(a) a.begin(), a.end()
template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> &a) {
  for (size_t i = 0; i < a.size(); ++i) os << (i > 0 ? " " : "") << a[i];
  return os << '\n';
}
template <typename T>
std::istream &operator>>(std::istream &is, std::vector<T> &a) {
  for (T &x : a) { is >> x; }
  return is;
}


constexpr int INF = 0x3f3f3f3f;

int n, d, p[1001], q[1001];

bool c(int x) {
  vector<vector<int>> dp(d + 1, vector<int>(n, -INF));
  rep(i, 0, n) dp[0][i] = 0;

  rep(k, 0, d) {
    vector<int> l(n, -INF), r(n, -INF);
    rep(i, 0, n - 1) l[i + 1] = max(l[i], dp[k][i]);
    rrep(i, 1, n) r[i - 1] = max(r[i], dp[k][i]);
    rep(i, 0, n) {
      int mx = max(l[i], r[i]);
      if (mx - p[i] >= x) { dp[k + 1][i] = mx - p[i] + q[i]; }
    }
  }
  int res = -INF;
  rep(i, 0, n) res = max(res, dp[d][i]);
  return res > -INF;
}

int main() {
  cin.tie(0)->sync_with_stdio(0);
  cin >> n >> d;
  rep(i, 0, n) cin >> p[i] >> q[i];

  int l = -INF, r = 0;
  while (r - l > 1) {
    int m = (l + r) / 2;
    if (c(m))
      l = m;
    else
      r = m;
  }
  cout << l << '\n';
  return 0;
}