#include <bits/stdc++.h>
using namespace std;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
template<int mod>istream &operator>>(istream &is,static_modint<mod> &a){long long b;is>>b;a=b;return is;}
istream &operator>>(istream &is,modint &a){long long b;cin>>b;a=b;return is;}
#endif
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) static_cast<void>(0)
#define debugg(...) static_cast<void>(0)
template<typename T1,typename T2>ostream &operator<<(ostream &os,const pair<T1,T2>&p){os<<p.first<<' '<<p.second;return os;}
#endif
using ll=long long;
using ull=unsigned long long;
using P=pair<ll,ll>;
template<typename T>using minque=priority_queue<T,vector<T>,greater<T>>;
template<typename T>bool chmax(T &a,const T &b){return (a<b?(a=b,true):false);}
template<typename T>bool chmin(T &a,const T &b){return (a>b?(a=b,true):false);}
template<typename T1,typename T2>istream &operator>>(istream &is,pair<T1,T2>&p){is>>p.first>>p.second;return is;}
template<typename T>istream &operator>>(istream &is,vector<T> &a){for(auto &i:a)is>>i;return is;}
template<typename T1,typename T2>void operator++(pair<T1,T2>&a,int n){a.first++,a.second++;}
template<typename T1,typename T2>void operator--(pair<T1,T2>&a,int n){a.first--,a.second--;}
template<typename T>void operator++(vector<T>&a,int n){for(auto &i:a)i++;}
template<typename T>void operator--(vector<T>&a,int n){for(auto &i:a)i--;}
#define reps(i,a,n) for(int i=(a);i<(n);i++)
#define rep(i,n) reps(i,0,n)
#define all(x) x.begin(),x.end()
#define pcnt(x) __builtin_popcount(x)
ll myceil(ll a,ll b){return (a+b-1)/b;}
template<typename T,size_t n,size_t id=0>
auto vec(const int (&d)[n],const T &init=T()){
  if constexpr (id<n)return vector(d[id],vec<T,n,id+1>(d,init));
  else return init;
}
int op(int x,int y){return max(x,y);}
int e(){return 0;}
int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  clock_t start=clock();
  int n,k;
  cin>>n>>k;
  vector<pair<int,int>>a(n);
  cin>>a;
  vector<int>z;
  z.reserve(n*2);
  rep(i,n)z.push_back(a[i].first),z.push_back(a[i].second);
  sort(all(z));
  z.erase(unique(all(z)),z.end());
  sort(all(a),[](pair<int,int>x,pair<int,int>y){return x.second<y.second;});
  auto b=a;
  rep(i,n){
    a[i].first=lower_bound(all(z),a[i].first)-z.begin();
    a[i].second=lower_bound(all(z),a[i].second)-z.begin();
  }
  mt19937 mt(998244353);
  int ans=1e9;
  while(clock()-start<1900000){
    int id=min(mt()%n,mt()%n);
    segtree<int,op,e>seg(z.size());
    reps(i,id,n){
      int g=seg.prod(0,a[i].first+1);
      if(g==k-1){
        chmin(ans,b[i].second-b[id].first);
        break;
      }
      seg.set(a[i].second,g+1);
    }
  }
  if(ans==1e9)ans=-1;
  cout<<ans<<endl;
}