#include <fstream>

using namespace std;
ifstream cin("branza.in");
ofstream cout("branza.out");
int v[100000],dq[100000];

int main()
{
   int n,s,t,suma=0,p;
   t++;
   cin>>n>>s>>t;
   int st=0,dr=-1;
   for(int i=0;i<n;i++){
    cin>>v[i]>>p;
    if(i>=t&&dq[st]==i-t){
    st++;
    }
    while(st<=dr&&v[i]&&v[i]<=v[dq[dr]]+s*(i-dq[dr])){
    dr--;
    }
    dq[++dr]=i;
        suma+=p*(v[dq[st]]+s*(i-dq[st]));
   }
   cout<<suma;
    return 0;
}