#include <bits/stdc++.h>
#include <atcoder/all>
#include <boost/polygon/point_data.hpp>
#include <boost/polygon/voronoi.hpp>
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define all(x) begin(x),end(x)
#define sz(x) (int)(x).size()
using namespace std;
using namespace atcoder;
using ll=long long;
using ld=long double;
using vll=vector<ll>;
using vvll=vector<vll>;
using vi=vector<int>;
using vvi=vector<vi>;
using pll=pair<ll,ll>;
using pi=pair<int,int>;

// using mint=modint998244353;
// using mint2=static_modint<2>;

// using BoostPoint=boost::polygon::point_data<int>;
// using Voronoi=boost::polygon::voronoi_diagram<double>;

int main()
{
  	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	ll N,D;
	cin>>N>>D;
	vector<pll>v(N);
	for(auto&[b,a]:v)cin>>a>>b;
	sort(v.rbegin(),v.rend());
	ll t=0,cnt=0;
	for(auto&[b,a]:v){
		cnt+=a;
		if(cnt>D){
			t=b;
			break;
		}
	}
	ll f=t;
	vector<pll>e;
	for(auto&[b,a]:v){
		if(b<=t)break;
		ll k=b-t;
		f+=a*((k-1)/D+1);
		ll r=(k-1)%D+1;
		if(r<D)e.push_back({r,a});
	}
	sort(all(e));
	ll ans=f,saved=0;
	for(auto [r,a]:e){
		saved+=a;
		ans=min(ans,f+r-saved);
	}
	cout<<ans<<'\n';
}