/******************************************************************************

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*******************************************************************************/
#include <iostream>
#include <algorithm>
#include <fstream>
using namespace std;
ifstream fin("lupu.in");
ofstream fout("lupu.out");
int n,x,l,d,a,v[100005],s;
struct fa
{
    int dist;
    int lana;
};
bool comp(fa a ,fa b)
{
    if(a.lana>b.lana){
        return 1;
    }
    if(a.lana==b.lana)
    {
        if(a.dist<b.dist)
        {
            return 1;
        }
    }
    return 0;
}
int main()
{
    fin>>n>>x>>l;
    fa vi[n+2];
    for(int i=1;i<=n;i++)
    {
        fin>>d>>a;
        vi[i].lana=a;
        vi[i].dist=(x-d)/l;
    }
    sort(vi+1,vi+n+1,comp);
    for(int i=1;i<=n;i++)
    {
        if(v[vi[i].dist]==0){v[vi[i].dist]=vi[i].lana;}
        else{
            for(int j=vi[i].dist-1;j>=0;j--)
            {
                if(v[j]==0){v[j]=vi[i].lana;break;}
            }
        }
    }
    for(int i=0;i<=x/l+1;i++)
    {
        s=s+v[i];
    }
    fout<<s;
    fin.close();
    fout.close();
    return 0;
}