// UUID: 581e3a58-1b70-4e8c-9cec-11b0bea3c091
#include <bits/stdc++.h>
using namespace std;
#define int long long

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int n,k;
    cin >> n >> k;

    vector<pair<int,bool>>v;
    v.reserve(n*2);

    int fds = 0, bds = 0, bc = 0, fc = 0;
    for(int i = 0; i < n; i++){
        int l,r;
        cin >> l >> r;
        fds+= l+k-1;
        fc++;
        v.push_back({l+k-1,0});
        v.push_back({r,1});
    }
    sort(v.begin(), v.end());
    fds-= v.front().first * fc;
    int ans = fds;
    v.push_back({INT_MAX, 1});
    for(int i = 0; i < n*2; i++){
        if(v[i].second){
            bc++;
        }
        else fc--;
        //cout << bds << ' ' << fds << '\n';
        fds+= fc*(v[i].first-v[i+1].first);
        bds-= bc*(v[i].first-v[i+1].first);
        ans = min(ans, bds+fds);
    }
    cout << ans;
}