#include<fstream>
#include<algorithm>
using namespace std;
ifstream fi("lupu.in");
ofstream fo("lupu.out");

struct oaie{
       int dist;
       int profit;
       int timp;
};

const int MAX_N = 100005;
oaie a[MAX_N];
int i,j,n,X,L;
int sol=0;

bool comp(const oaie &A, const oaie &B){
     if(A.timp==B.timp) return (A.profit>B.profit);
     else return (A.timp<B.timp);
}

int main(){
    fi>>n>>X>>L;
    for(i=1;i<=n;i++){
                      fi>>a[i].dist>>a[i].profit;
                      a[i].timp=(X-a[i].dist)/L;
                     }
    
    sort(a+1,a+n+1,comp);
    
    for(i=1;i<=n;i++)
       {
        sol+=a[i].profit;
        
        for(j=i+1; j<=n && a[i].timp==a[j].timp; ++j);
        i=j-1;
       }
    
    fo<<sol;
    
    fi.close();
    fo.close();
    return 0;
}