#ifdef NACHIA
#define _GLIBCXX_DEBUG
#else
// disable assert
#define NDEBUG
#endif
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
using ll = long long;
const ll INF = 1ll << 60;
#define REP(i,n) for(ll i=0; i<ll(n); i++)
template <class T> using V = vector<T>;
template <class A, class B> void chmax(A& l, const B& r){ if(l < r) l = r; }
template <class A, class B> void chmin(A& l, const B& r){ if(r < l) l = r; }

void testcase(){
  ll N, D; cin >> N >> D;
  V<pair<ll,ll>> BA(N);
  for(auto& [b,a] : BA) cin >> a >> b;
  sort(BA.rbegin(), BA.rend());
  
  ll cnt = 0;
  ll offset_1 = 0;
  for(auto [b,a] : BA) cnt += a;
  while(cnt >= D){
    auto [b,a] = BA.back();
    cnt -= a;
    offset_1 = b;
    BA.pop_back();
  }

  ll offset_2 = 0;
  for(auto& [b,a] : BA){
    b -= offset_1;
    offset_2 += b / D * a;
    b %= D;
  }
  sort(BA.begin(), BA.end());

  // cout << "offset_1 = " << offset_1 << " , offset_2 = " << offset_2 << endl;
  // for(auto [b,a] : BA) REP(t,a) cout << b << " "; cout << endl;

  ll ans = cnt;
  ll pt = cnt;
  for(auto [b,a] : BA){
    pt -= a;
    chmin(ans, pt + b);
  }

  ans += offset_1 + offset_2;

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

int main(){
  cin.tie(0)->sync_with_stdio(0);
  testcase();
  return 0;
}