#include<bits/stdc++.h>
using namespace std;
ifstream fin("lupu.in");
ofstream fout("lupu.out");

struct elem
{
    int dist,cost;
}v[100001];

inline bool cmp(const elem a,const elem b)
{
   if(a.dist==b.dist)
    return a.cost<b.cost;
   return a.dist<b.dist;
}

int main()
{
    int n,x,l,i,a,b,ans=0,j,k;
    fin>>n>>x>>l;
    for(i=1;i<=n;i++)
    {
        fin>>v[i].dist>>v[i].cost;
    }
    sort(v+1,v+n+1,cmp);
    long long sans=0;
    int ind=1;
    for(i=0;i<=x;i+=l)
    {
        int maxim=0;
        int k=0;
        while(ind<n && v[ind].dist<=i)
        {
            if(v[ind].cost>maxim)
                maxim=v[ind].cost;
            ind++;
        }
       ans+=maxim;
    }
    fout<<ans;
    return 0;
}