#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;


template<typename T>
vector<vector<T>> vec2d(int n, int m, T v){
    return vector<vector<T>>(n, vector<T>(m, v));
}

template<typename T>
vector<vector<vector<T>>> vec3d(int n, int m, int k, T v){
    return vector<vector<vector<T>>>(n, vector<vector<T>>(m, vector<T>(k, v)));
}

template<typename T>
void print_vector(vector<T> v, char delimiter=' '){
    if(v.empty()) {
        cout << endl;
        return;
    }
    for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter;
    cout << v.back() << endl;
}


using P = pair<int, int>;
const int INF = 1e9;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    int n, d; cin >> n >> d;
    vector<int> p(n), q(n);
    for(int i = 0; i < n; i++) cin >> p[i] >> q[i];
    auto judge = [&](int lb) -> bool{
        // debug_value(lb);
        auto dp = vec2d(d, n, -INF);
        for(int i = 0; i < n; i++) {
            if(-p[i] >= lb) dp[0][i] = q[i]-p[i];
        }
        for(int i = 1; i < d; i++){
            int mx1 = -INF, mx2 = -INF;
            for(int j = 0; j < n; j++){
                if(dp[i-1][j] > mx1){
                    mx2 = mx1;
                    mx1 = dp[i-1][j];
                }else if(dp[i-1][j] > mx2){
                    mx2 = dp[i-1][j];
                }
            }
            for(int j = 0; j < n; j++){
                if(dp[i-1][j] == mx1){
                    if(mx2-p[j] >= lb) dp[i][j] = mx2-p[j]+q[j];
                }else{
                    if(mx1-p[j] >= lb) dp[i][j] = mx1-p[j]+q[j];
                }
            }
        }
        for(int j = 0; j < n; j++){
            if(dp[d-1][j] != -INF) return true;
        }
        return false;
    };

    int l = 0, r = 1e9;
    while(r-l > 1){
        int x = (l+r)/2;
        if(judge(-x)) r = x;
        else l = x;
    }
    cout << -r << endl;
}