#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> ii;
typedef vector<ii> vii;
#define PB push_back
#define X first
#define Y second
#define all(x) (x).begin(), (x).end()
const int MAXN = 3e5 + 7;
int n, k;
vii ev;
multiset<int> s;
int le[MAXN], ri[MAXN];
void solve(){
cin >> n >> k;
for(int i=1; i<=n; i++){
cin >> le[i] >> ri[i];
ev.PB({le[i], i});
ev.PB({ri[i], -i});
}
sort(all(ev));
int ans = 0;
for(auto &x : ev){
if(x.Y > 0){
s.insert(ri[x.Y]);
if((int)s.size() > k) s.erase(s.begin());
}else if(*s.begin() == x.X) s.erase(s.begin());
if((int)s.size() == k) ans = max(ans, *s.begin() - x.X);
}
cout << ans << "\n";
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
solve();
return 0;
}
