#include <fstream>
#include <set>
#include <algorithm>
struct a
{
    int distanta,lana;
}
v[200005];
using namespace std;
ifstream fin("lupu.in");
ofstream fout("lupu.out");
int n,dmax,dist,Tmax,t[200005],s;
int main()
{
    multiset <int> my_set;
    fin>>n>>dmax>>dist;
    for(int i=1;i<=n;++i)
        fin>>v[i].distanta>>v[i].lana;
        for(int i=1;i<=n;++i)
        {
            t[i]=(dmax-v[i].distanta)/dist+1;
            if(t[i]>Tmax)
                Tmax=t[i];
        }
        for(int i=1;i<=Tmax;++i)
        {
            for(int j=1;j<=n;++j)
        {
            if(t[j]==i)
                {int k=v[j].lana;
                    my_set.insert(k);}
        }
        multiset <int> :: iterator it=my_set.end();
        --it;
        s+=*it;
        my_set.clear();
        }
        fout<<s;
    return 0;
}