#include <iostream>
#include <fstream>

using namespace std;

int i,j,k,l;
int n,m,s;
int t[5010],f[5010],w[5010];
int tmp;

int main()
{
	ifstream fin("batch.in");
	ofstream fout("batch.out");
	
	fin>>n>>s;
	
	for (i=1;i<=n;i++)
		fin>>t[i]>>f[i];
	
	f[n+1]=t[n+1]=0;
	for (i=n;i>=1;i--)
	{
		f[i]=f[i]+f[i+1];
		t[i]=t[i]+t[i+1];
	}
	
	w[n]=f[n]*t[n];
	w[n+1]=0;
	
	for (i=n-1;i>=1;i--)
	{
		w[i]=f[i]*t[i];
		for (j=n+1;j>i;j--)
			if ( (tmp= (w[j]+(s+t[i]-t[j])*f[j]+(f[i]-f[j])*(t[i]-t[j])) )<w[i] )
				w[i]=tmp;
	}
	
	fout<<w[1]+s*f[1]<<endl;
	
	fin.close();
	fout.close();
	
	return 0;
}