#include<fstream>
using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");
int G,W,cost,energie,i,e,c,cf;
int a_()
{
  e=energie;
  c=cost;
  while(e<W)
  { e+=e;
    c+=c;
  }
  if(c<cf)
  {
   cf=c;
  }
 return cf;
}

int main()
{ fin>>G;
  fin>>W;
  fin>>energie;
  fin>>cost;
  e=energie;
  c=cost;
  while(e<W)
  { e+=e;
    c+=c;
  }
  cf=c;
  for(i=1;i<G;i++)
  { fin>>energie;
    fin>>cost;
	a_();
  }
  fout<<cf;
return 0;
}