#include <iostream>

using namespace std;
typedef long long ll;
ll p[1010],q[1010],dp[1010][1010],l[1010],r[1010],INF = 10000000000000;
int main(){
    int i,j,n,d; cin >> n >> d;
    for(i=0;i<n;i++) cin >> p[i] >> q[i];
    ll le = -INF,ri = INF;
    while(ri - le>1){
        ll mid = (le + ri)/2;
        for(j=0;j<n;j++){
            if(-p[j]>=mid) dp[0][j] = q[j] - p[j];
            else dp[0][j] = -INF;
        }
        l[0] = -INF,r[n] = -INF;
        for(j=1;j<=n;j++) l[j] = max(l[j - 1],dp[0][j - 1]);
        for(j=n - 1;j>=0;j--) r[j] = max(r[j + 1],dp[0][j]);
        for(i=1;i<d;i++){
            for(j=0;j<n;j++){
                ll mx = max(l[j],r[j + 1]);
                if(mx - p[j]>=mid) dp[i][j] = mx + q[j] - p[j];
                else dp[i][j] = -INF;
            }
            l[0] = -INF,r[n] = -INF;
            for(j=1;j<=n;j++) l[j] = max(l[j - 1],dp[i - 1][j - 1]);
            for(j=n - 1;j>=0;j--) r[j] = max(r[j + 1],dp[i - 1][j]);
        }
        int cnt = 0;
        for(j=0;j<n;j++){
            if(dp[d - 1][j]!=-INF) cnt++;
        }
        if(cnt) le = mid;
        else ri = mid;
    }
    cout << le << endl;
}