#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 l = -1001001001,r = 0;
    while (l+1 < r) {
        int mid = (l+r)/2;
        vector<vector<int>>dp(D+1,vector<int>(N,-1001001001));
        for(int i = 0; i < N; i++) {
            dp[0][i] = 0;
        }
        for(int i = 0; i < D; i++) {
            vector<int>lmx(N+1,-1001001001),rmx(N+1,-1001001001);
            for(int j = 0; j < N; j++) {
                lmx[j+1] = max(lmx[j],dp[i][j]);
            }
            for(int j = N; j >= 1; j--) {
                rmx[j-1] = max(rmx[j],dp[i][j-1]);
            }
            for(int j = 0; j < N; j++) {
                if(max(lmx[j],rmx[j+1])-P[j] >= mid) {
                    dp[i+1][j] = max(dp[i+1][j],max(lmx[j],rmx[j+1])-P[j]+Q[j]);
                }
            }
        }
        int mx = *max_element(dp[D].begin(),dp[D].end());
        if(mx >= mid) {
            l = mid;
        }
        else {
            r = mid;
        }
    }
    cout << l << endl;
}