//#include <atcoder/all>
//using namespace atcoder;
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(v) v.begin(),v.end()
typedef long long ll;
#define int ll
using vi = vector<int>;
using vs = vector<string>;
using P = pair<int,int>;
template<typename T> bool chmax(T &a, const T b) {if (a < b) {a = b; return true;} else return false; }
template<typename T> bool chmin(T &a, const T b) {if (a > b) {a = b; return true;} else return false; }
const int INF = 1e18;
//using mint = modint1000000007;
//using mint = modint998244353;

signed main() {
   cin.tie(0);
   ios_base::sync_with_stdio(false);
   cout << fixed << setprecision(20);

   int n,d;cin>>n>>d;
   vector<P> can,de;
   rep(i,n){
       int p,q;
       cin>>p>>q;
       if(p<=q)can.push_back({p,q});
       de.push_back({p-q,q});
   }
   P one,two;
   if(can.size()<2){
       sort(all(de));
       one = de[0];
       two = de[1];
       one.first+=one.second;
       two.first+=two.second;
   }
   else{
       sort(all(can));
       one = can[0];
       two = can[1];
   }
   //cout << one.first<<" "<<one.second <<"\n";
   //cout << two.first<<" "<<two.second <<"\n";
   int tmp=0;
   int ans = 0;
   rep(i,n){
       if(i%2==0){
           tmp-=one.first;
           chmin(ans,tmp);
           tmp+=one.second;
       }
       else{
           tmp-=two.first;
           chmin(ans,tmp);
           tmp+=two.second;
       }
   }
   cout<<ans<<endl;
   return 0;
}