#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pll pair<int,int>
#define fi first
#define se second
#define lowbit(x) (x&(-x))
typedef long long LL;
typedef unsigned long long ull;
int n,m,k;
int res;
const int N=1e6+10,M=1e5,mod=998244353;
const double eps=1e-6,inf=1e8;

int bit[N],dap[N];
int sum[N];
int dp[N];

struct stu
{
	int hp,ad;
	bool operator<(const stu &B) const
	{
		if(ad==B.ad) return hp<B.hp;
		else return ad<B.ad;
	}
}st[N];

void modify(int id,int x)
{
	if(bit[id]<x) return;
	bit[id]=dap[id]=x;
	while(id<=M)
	{
		bit[id]=x;
		for(int i=1;i<lowbit(id);i<<=1)
		{
			bit[id]=min(bit[id],bit[id-1]);
		}
		id+=lowbit(id);
	}
}

int quer(int l,int r)
{
	int res=dap[r];
	while(l<=r)
	{
		int lr=r-(r&-r)+1;
		if(lr>=l) res=min(res,bit[r]),r=lr-1;
		else res=min(res,dap[r]),r--;
	}
	return res;
}

int qes(int id)
{
	//cout<<id<<"---------------------------"<<endl;
	int ma=1e18;
	for(int i=m;i<st[id].ad;i++)
	{
		int t=st[id].hp/i;
		int j=st[id].hp/t;
		j=max(j,st[i].ad-1);
		if(i!=j&&st[id].hp%j==0) j--;
		else if(i==j&&st[id].hp%i==0) t--;
		//cout<<i<<" "<<j<<" "<<quer(i,j)<<" "<<t<<" "<<quer(i,j)+t*st[id].ad<<endl;
		if(ma>quer(i,j)+t*st[id].ad)
		{
			ma=quer(i,j)+t*st[id].ad;
		}
	}
	return ma+sum[id-1];
}

void solve() {
	memset(bit,0x3f,sizeof bit);
	memset(dap,0x3f,sizeof dap);
	cin>>n>>m;
	for(int i=1;i<=n;i++) cin>>st[i].ad>>st[i].hp;
	sort(st+1,st+1+n);
	//for(int i=1;i<=n;i++) cout<<"---"<<st[i].ad<<" "<<st[i].hp<<endl;
	int mx=max(m,st[n].ad);
	for(int i=1;i<=n;i++)
	{
		sum[i]=(st[i].hp/mx)*st[i].ad;
		if(st[i].hp%mx==0) sum[i]-=st[i].ad;
		sum[i]+=sum[i-1];
	}
	int fro=0;
	while(fro<n&&st[fro].ad<=m) fro++;
	modify(m,0);
	for(int i=fro;i<=n;i++)
	{
		dp[i]=qes(i);
		//cout<<i<<" "<<dp[i]<<"----"<<dp[i]-sum[i]<<endl;
		modify(st[i].ad,dp[i]-sum[i]);
	}
	cout<<dp[n]<<endl;
}

signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int T=1;
    //cin>>T;
    while(T--)
    {
        solve();
    }
    return 0;
}
/*
4 1
3 2
4 4
5 6
1 6

3 1
3 2
4 4
1 6
*/