#include <bits/stdc++.h>
    using namespace std;
    #include <math.h>
    #include <iomanip>
    #include <cstdint>
    #include <string>
    #include <sstream>
    template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
    template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
    #define rep(i,n) for (int i = 0; i < (n); ++i)
    typedef long long ll;
    typedef long double ld;
    typedef unsigned long long ull;
    using P=pair<ll,ll>;
    const ll INF=1001001001;
    const int mod=998244353;
    
    void solve(){
        int n,d;
        cin>>n>>d;
        vector<int>p(n+1),q(n+1);
        for(int i=1;i<=n;i++)cin>>p[i]>>q[i];
        
        auto f=[&](int mid){
            vector<vector<ll>>dp(d+1,vector<ll>(n+1,-INF));
            rep(i,d){
                for(int j=1;j<=n;j++){
                    for(int k=1;k<=n;k++){
                        if(j!=k&&(i==0?0:dp[i][j])-p[i]>=mid){
                            chmax(dp[i+1][k],(i==0?0:dp[i][j])+q[k]-p[k]);
                        }
                    }
                }
            }
            rep(i,n){
                if(dp[n][i]>=mid){return true;}
            }
            return false;
        };
        int l=-INF,r=0;
        while(r-l>1){
            int mid=(l+r)/2;
            if(f(mid)){l=mid;}
            else{r=mid;}
        }
        cout<<l<<endl;
    } 

    int main(){
        ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        
        solve();

        return 0;
    }