#include<bits/stdc++.h>
using namespace std;
#define Maxh 200000
#define int long long
#define ls x<<1
#define rs x<<1|1
#define fi first
#define se second
#define pii pair<int,int> 
int n,a0;
struct node{
	int a,h;
	friend bool operator<(node x,node y){
		return x.a<y.a;
	}
}b[200020];
double slope(pii x,pii y){
	return 1.0*(x.se-y.se)/(x.fi-y.fi);
}
int calc(pii x,int y){
	return x.se-y*x.fi;
}
struct tree{
	int hd;
	vector<pii>v;
}tr[800080];
void upd(int x,pii k){
	while(tr[x].v.size()-tr[x].hd>1){
		pii v1=tr[x].v[tr[x].v.size()-1];
		pii v2=tr[x].v[tr[x].v.size()-2];
		if(k.fi==v1.fi){
			if(k.se>=v1.se) return ;
			else tr[x].v.pop_back();
		}else{
			if(slope(k,v1)<slope(k,v2)) break;
			tr[x].v.pop_back();
		}
	}
	tr[x].v.push_back(k);
}
int qry(int x,int k){
	if(tr[x].v.size()-tr[x].hd<=0) return 1e18;
	while(tr[x].v.size()-tr[x].hd>1){
		pii v1=tr[x].v[tr[x].hd],v2=tr[x].v[tr[x].hd+1];
		if(slope(v1,v2)<=k) break;
		tr[x].hd++;
	}
	return calc(tr[x].v[tr[x].hd],k);
}
void update(int x,int l,int r,int L,int R,pii v){
	if(l>=L&&r<=R) return upd(x,v),void();
	int mid=l+r>>1;
	if(L<=mid) update(ls,l,mid,L,R,v);
	if(R>=mid+1) update(rs,mid+1,r,L,R,v);
}
int query(int x,int l,int r,int k,int v){
	int tmp=qry(x,v);
	if(l==r) return tmp;
	int mid=l+r>>1;
	if(k<=mid) tmp=min(tmp,query(ls,l,mid,k,v));
	else tmp=min(tmp,query(rs,mid+1,r,k,v));
	return tmp;
}
void alter(int x,int y){
	for(int i=1;i<=Maxh;i+=x){
		update(1,1,Maxh,i,min((int)Maxh,i+x-1),{(i-1)/x,y});
	}
}
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(nullptr);
	cin>>n>>a0;
	for(int i=1;i<=n;i++){
		cin>>b[i].a>>b[i].h;
	}
	sort(b+1,b+1+n);
	int st=upper_bound(b+1,b+1+n,node{a0,0})-b;
	alter(a0,0);
	int minn=1e18;
	for(int i=st;i<=n;i++){
		int x=query(1,1,Maxh,b[i].h,-b[i].a);
		x-=(b[i].h-1)/b[n].a*b[i].a;
		minn=min(minn,x);
		if(b[i+1].a!=b[i].a){
			alter(b[i].a,minn);
			if(i!=n) minn=1e18;
		}
	}
	int ans=0;
	for(int i=1;i<=n;i++) ans+=(b[i].h-1)/max(b[n].a,a0)*b[i].a;
	if(a0<=b[n].a) ans+=minn;
	cout<<ans;
	return 0;
}