#include<iostream>
using namespace std;
int n,s,c[10001],y[10001],m;//在生产机器资金最少那天生产剩下所有机器，一直往前分割;
long long x;
bool flag=false;
int main()
{
    cin>>n>>s;
    for(int i=1;i<=n;i++)
    {
        cin>>c[i]>>y[i];
    }
    for(int i=1;i<=n;i++)
    {
        if(y[i]<=y[i+1]&&(c[i]-c[i+1]>5||c[i+1]-c[i]>5))
        {
            if(m>=1)x+=c[i-m]*y[i]+y[i]*s*m;
            else x+=c[i]*(y[i]+y[i+1])+y[i+1]*s;
            flag=true;
            m+=1;
        }
        if(flag==true)continue;
        else
        {
            x+=c[i]*y[i];
            flag=false;
            m=0;
        }
    }
    cout<<x<<endl;
    system("pause");
    return 0;
}

help!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!