#include <algorithm>
#include <iostream>
#include <numeric>
#include <vector>

using namespace std;

using ll = long long;

struct monster {
    ll attack;
    ll hits;

    bool operator <(monster const& rhs) const {
        return attack * rhs.hits < rhs.attack * hits;
    }
};

int main() {
    ll n, p;
    cin >> n >> p;

    vector<monster> monsters(n);

    for (monster& m : monsters) {
        ll a, d;
        cin >> a >> d;

        m = { a, (d + p - 1) / p };
    }

    sort(monsters.begin(), monsters.end());

    ll ans = 0;
    ll dmg = 0;

    for (monster const& m : monsters) {
        dmg += m.attack;

        ans += dmg * m.hits;
    }

    ans -= dmg;

    cout << ans << "\n";
}