#include <bits/stdc++.h>
using namespace std;
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 ub = 0, lb = -1000000000;
    int INF = 2000000000;
    while(ub - lb > 1){
        int mid = (ub + lb) / 2;
        vector<vector<int>> dp(D, vector<int>(N, -INF));
        bool f = false;
        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, -INF), R(N + 1, -INF);
            for(int j = 0; j < N; j++){
                L[j + 1] = max(L[j], dp[i][j]);
                R[N - 1 - j] = max(R[N - j], dp[i][N - 1 - j]);
            }
            for(int j = 0; j < N; j++){
                int t = max(R[j + 1], L[j]);
                if(t - P[j] >= mid) dp[i + 1][j] = t - P[j] + Q[j];
            }
        }
        for(int i = 0; i < N; i++){
            if(dp[D - 1][i] != -INF) f = true;
        }
        if(f) lb = mid;
        else ub = mid;
    }
    cout << lb << endl;
}