#include <bits/stdc++.h>
#define ll long long
using namespace std;


int main() {
    ios::sync_with_stdio(0); cin.tie(0);
    freopen("lupu.in","r",stdin);
    freopen("lupu.out","w",stdout);
    long long n,x,l;
    cin >> n >> x >> l;
    map<long long,long long>c;
    for(int i = 0;i<n;i++){
        long long d;
        cin >> d;
        long long v;
        cin >> v;
        if(x >= d){
            long long pasi = x-d;
            long long ans = pasi / l;
      
            c[ans] = max(c[ans],v);
        }
      
    }
    long long ans = 0;
    for(auto p : c){
        ans += p.second;
    }
    cout << ans;

    return 0;
}