#include <fstream>

using namespace std;
const int N=100000;
int d[N],v[N],n,k;
ifstream cin("branza.in");
ofstream cout("branza.out");
int main()
{
    long long n,i,k,s=0,p,t,sum=0;
    cin>>n>>s>>t;
    ++k;
    int st=0,dr=-1;
    for(i=0;i<n;i++)
    {
      cin>>v[i];
      cin>>p;
      if(d[st]==i-k)
      {
        st++;
      }
      while(st<=dr&&v[i]<=v[d[dr]]+(i-d[dr])*s)
      {
        dr--;
      }
      d[++dr]=i;
          sum+=p*(v[d[st]]+(i-d[st])*s);
    }
    cout<<sum;
    return 0;
}