#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 ti;
int quer(int l,int r)
{
	ti++;
	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<<"---------------------------"<<st[id].ad<<endl;
	int ma=1e18;
	for(int i=m;i<st[id].ad;i++)
	{
		int t=st[id].hp/i;
		//cout<<t<<endl;
		int j;
		if(t)
		j=st[id].hp/t;
		else j=st[id].ad-1;
		j=min(j,st[id].ad-1);
		//cout<<i<<" "<<j<<" "<<t<<endl;
		//cout<<quer(i,j)<<endl;
		if(ma>quer(i,j)+t*st[id].ad)
		{
			ma=quer(i,j)+t*st[id].ad;
		}
		t--;
		if(st[id].hp%j==0) ma=min(ma,dap[j]+t*st[id].ad);
		i=j;
		//cout<<"ED"<<endl;
	}
	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]) sum[i]-=st[i].ad;
		sum[i]+=sum[i-1];
		if(sum[i]<0) cout<<"----"<<endl;
	}
	int fro=1;
	while(fro<=n&&st[fro].ad<=m) fro++;
	if(fro>n)
	{
		cout<<sum[n]<<endl;
		return;
	}
	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<<ti<<endl;
	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


26 679
84191 46042
81916 66659
74636 72443
10252 57443
21838 54620
84896 58466
20832 29643
45949 20576
50399 51434
56472 90759
68909 94348
39459 1731
81207 17614
26465 11775
93861 24936
25017 64663
21042 37570
32903 68583
68840 58347
93849 108419
10190 77131
10595 1959
57163 59047
16066 89850
7001 679
98290 7000

5 11
1 100000
1 100000
1 100000
1 100000
1 100000
*/