#include <bits/stdc++.h>

using namespace std;
#define int long long
map<int,int>m;
signed main()
{
ifstream cin("lupu.in");
ofstream cout("lupu.out");
int n,x,l;
cin>>n>>x>>l;
vector<int>v(n);
vector<int>v2(n);
vector<int>f;
for(int i=0;i<n;i++)
{
    cin>>v[i]>>v2[i];
    if(v[i]>x)
    continue;
    int k=(x-v[i])/l+1;
    if(m.find(k)==m.end())
    {
        m[k]=v2[i];
        f.push_back(k);
    }
    else
    {
        int c=m[k];
        m[k]=max(c,v2[i]);
    }
}
int s=0;
for(int i=0;i<f.size();i++)
{
    s=s+m[f[i]];
}
cout<<s;
    return 0;
}