#include<bits/stdc++.h>
using namespace std;
#define ll long long 
#define ull unsigned long long
#define sort stable_sort 
#define endl '\n'
ll f[300010],t[300010],c[300010],k[300010],p[300010],tmp[300010],n,s;
deque<ll>q;
bool cmpk(ll a,ll b)
{
	return k[a]<k[b];
}
ll x(ll i)
{
	return c[i];
}
ll y(ll i)
{
	return f[i];
}
bool cmpx(ll a,ll b)
{
	return (x(a)==x(b))?(y(a)<y(b)):(x(a)<x(b));
}
void cdq(ll l,ll r)
{
	if(l==r)  return;
	ll mid=(l+r)/2;
	for(ll i=l,x=l,y=mid+1;i<=r;i++)
	{
		if(p[i]<=mid)
		{
			tmp[x]=p[i];  x++;
		}
		else
		{
			tmp[y]=p[i];  y++;
		}
	}
	for(ll i=l;i<=r;i++)  p[i]=tmp[i];
	cdq(l,mid);
	q.clear();
	for(ll i=l;i<=mid;i++)
	{
		while(q.size()>=2&&(y(q.back())-y(q[q.size()-2]))*(x(p[i])-x(q.back()))>=
							(y(p[i])-y(q.back()))*(x(q.back())-x(q[q.size()-2])))
			q.pop_back();
		q.push_back(p[i]);
	}
	for(ll i=mid+1;i<=r;i++)
	{
		while(q.size()>=2&&(y(q[1])-y(q.front()))<=k[p[i]]*(x(q[1])-x(q.front())))
			q.pop_front();
		f[p[i]]=min(f[p[i]],f[q.front()]+t[p[i]]*(c[p[i]]-c[q.front()])+s*(c[n]-c[q.front()]));
	}
	cdq(mid+1,r);
	sort(p+l,p+r+1,cmpx);
}
int main()
{
// #define Isaac
#ifdef Isaac
	freopen("in.in","r",stdin);
	freopen("out.out","w",stdout);
#endif
	cin>>n>>s;
	for(ll i=1;i<=n;i++)
	{
		cin>>t[i]>>c[i];  p[i]=i;
		t[i]+=t[i-1];  c[i]+=c[i-1];  k[i]=t[i]+s;
	}
	for(ll i=1;i<=n;i++)  f[i]=t[i]*c[i]+s*c[n];
	sort(p+1,p+1+n,cmpk);  cdq(1,n);
	cout<<f[n]<<endl;
	return 0;
}