#include<bits/stdc++.h>
using namespace std;
#define int long long
#define REP(i,m,n) for(int i=(m);i<(n);i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define all(a) a.begin(),a.end()
#define rall(c) (c).rbegin(),(c).rend()
#define mp make_pair
#define endl '\n'
//#define vec vector<ll>
//#define mat vector<vector<ll> >
#define fi first
#define se second
#define double long double
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
//typedef long double ld;
typedef complex<double> Complex;
const ll INF=1e9+7;
const ll MOD=998244353;
const ll inf=INF*INF;
const ll mod=MOD;
const ll MAX=200010;
const double PI=acos(-1.0);
typedef vector<vector<ll> > mat;
typedef vector<ll> vec;

 
void solve(){
    ll n,d;cin>>n>>d;
    vector<ll>p(n),q(n);
    rep(i,n){
        cin>>p[i]>>q[i];
    }
    ll l=0,r=inf;
    while(r-l>1){
        ll mid=(r+l)/2;
        vector<vector<ll> >dp(d,vector<ll>(n,-inf));
        rep(i,n){
            if(p[i]<=mid)dp[0][i]=q[i]-p[i];
        }
        REP(i,1,d){
            vector<ll>up(n,-inf);
            vector<ll>low(n,-inf);
            up[0]=dp[i-1][0];
            low[n-1]=dp[i-1][n-1];
            REP(j,1,n)up[j]=max(dp[i-1][j],up[j-1]);
            for(int j=n-2;j>+0;j--)low[j]=max(dp[i-1][j],low[j+1]);
            rep(j,n){
                ll a=-inf;
                if(j)a=up[j-1];
                ll b=-inf;
                if(j<n-1)b=low[j+1];
                ll ma=max(a,b);
                if(ma-p[j]>=-mid){
                    dp[i][j]=max(dp[i][j],ma+q[j]-p[j]);
                }
            }
        }
        bool f=0;
        rep(j,n){
            if(dp[d-1][j]>-inf){
                f=1;
            }
        }
        if(f)r=mid;
        else l=mid;
    }
    cout<<-r<<endl;
    
}

signed main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
}