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

int main() {
    ios::sync_with_stdio(false); in.tie(0); out.tie(0);
    
    int n, x ,l; in >> n >> x >> l;

    vector< multiset< int > > memo(x / l + 2, multiset< int >());
    for(int i = 0; i < n; ++i) {
        int d, a; in >> d >> a;

        memo[d / l + 1].insert(-a);
    }

    int ans = 0;
    for(int i = 1; i < x / l + 2; ++i) {
        ans += (-(*memo[i].begin()));
    }

    out << ans << "\n";

    in.close(); out.close();
 
    return 0;
}