#include <iostream>
#include <utility>
#include <vector>
#include <algorithm>
#include <cstring>
using namespace std;

struct Interval:pair<int,int>{
    int &l(){return first;}
    int &r(){return second;}
    int size(){return r()-l();}
};

Interval v[200];
vector<int> spare;

int main(){
    int n,p; cin>>n>>p;
    for (int i=0; i<n; i++){
        cin>>v[i].l()>>v[i].r();
    }
    for (int i=0; i<n; i++){
        for (int j=0; j<n; j++){
            if (v[i].l()<=v[j].l() and v[i].r()>v[j].r() or v[i].l()<v[j].l() and v[i].r()>=v[j].r()){
                spare.push_back(v[i].size());
                swap(v[i--],v[--n]); break;
            }
        }
    }
    sort(v,v+n);
    sort(spare.rbegin(),spare.rend());
    for (int i=1; i<spare.size(); i++) spare[i]+=spare[i-1];

    static int dp[201][201];
    memset(dp,0x80,sizeof dp);
    dp[0][0]=0;
    for (int i=0; i<spare.size(); i++) dp[0][i+1]=spare[i];

    for (int i=0; i<n; i++){
        for (int j=0; j<p; j++){
            if (dp[i][j]<0) continue;
            for (int k=i; k<n and v[k].l()<v[i].r(); k++){
                dp[k+1][j+1]=max(dp[k+1][j+1],dp[i][j]+v[i].r()-v[k].l());
            }
        }
    }
    cout<<dp[n][p]<<endl;
}