#include <bits/stdc++.h>
using namespace std;

#define rep(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define ALL(v) (v).begin(),(v).end()
using ll=long long int;
const int inf = 0x3fffffff; const ll INF = 0x1fffffffffffffff; const double eps=1e-12;
template<typename T>inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<typename T>inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}



int main(){
    int n,d;
    cin>>n>>d;
    vector<int> p(n),q(n);
    rep(i,0,n)cin>>p[i]>>q[i];

    using P=pair<int,int>;
    vector dp(d+1,vector<P>(n,{-inf,-inf}));
    rep(i,0,n){
        dp[1][i]={-p[i],q[i]-p[i]};
    }
    rep(j,1,d)rep(i,0,n){
        rep(to,0,n)if(i!=to){
            auto [x,y]=dp[j][i];
            chmin(x,y-p[to]);
            y+=q[to]-p[to];
            chmax(dp[j+1][to],P{x,y});
        }
    }
    int res=-inf;
    rep(i,0,n)chmax(res,dp[d][i].first);
    cout<<res<<'\n';
    return 0;
}