// UUID: 55f3e503-1d73-4f68-a84d-aae434fae6fc
#include <bits/stdc++.h>
using namespace std;

#define endl '\n'
#define pb push_back
#define iter(v) v.begin(), v.end()
#define riter(v) v.rbegin(), v.rend()
#define vi vector<int>
#define vb vector<bool>
#define vvi vector<vector<int>>
#define vvb vector<vector<bool>>
#define int long long

signed main() {
    ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int n,k;cin>>n>>k;
    vector<array<int, 2>> tv(n+1);
    vector<int> ends;
    ends.reserve(n*2+1);
    for(int i=1;i<=n;i++){
        cin >> tv[i][0] >> tv[i][1];
        ends.pb(tv[i][0]);
        ends.pb(tv[i][1] -k+1);
    }
    sort(iter(ends));
    int mincost = 0;
    int opt = ends[ends.size()/2];
    for(int i=1;i<=n;i++){
        if(tv[i][0] > opt) mincost += tv[i][0] - opt;
        if(tv[i][1] < opt + k-1) mincost += opt+k-1 - tv[i][1];
    }
    cout << mincost;

}