#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
using ll = long long;

int n, k, a = 1, b = 1e9, c;
ll ans = 0;
vector <int> L;
vector <int> R;

bool test(int l) {
    int r = l + k - 1, dif = 0;
    dif += n - (upper_bound(L.begin(), L.end(), l) - L.begin());
    dif -= upper_bound(R.begin(), R.end(), r) - R.begin();
    return (dif > 0 ? true : false);
}

int main()
{
    cin >> n >> k;
    L.resize(n);
    R.resize(n);
    for (int i = 0; i < n; i++) cin >> L[i] >> R[i];
    sort(L.begin(), L.end());
    sort(R.begin(), R.end());
    while (b - a > 1) {
        c = (a + b) / 2;
        (test(c) ? a = c : b = c);
    }
    int l = b, r = b + k - 1;
    for (int i : L) ans += (i > l ? i - l : 0);
    for (int i : R) ans += (i < r ? r - i : 0);
    cout << ans;
}