#include <bits/stdc++.h>
#define V vector
#define L(i,j,k) for(int i=(j);i<=(k);i++)
#define R(i,j,k) for(int i=(j);i>=(k);i--)
#define all(x) x.begin(),x.end()
#define sz(a) ((int)a.size())
#define pb push_back
using namespace std;
typedef long long ll;
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
template <typename T>
using indexed_set = tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
int main(){
int n,k;cin>>n>>k;
V<pair<ll,ll>>nu(n);
L(i,0,n-1){
cin>>nu[i].first>>nu[i].second;
}
sort(all(nu));
indexed_set<pair<ll,ll>>s;
int m=0;
ll ans=0;
L(i,0,n-1){
s.insert({nu[i].second,i});
m++;
if(m<k)continue;
auto it=s.find_by_order(m-k);
ans=max(ans,1ll*(it->first)-nu[i].first);
}
cout<<ans<<endl;
}
