#include <bits/stdc++.h>
using namespace std;
int n, x, d, nr, val, s, i;
int v[100005];
int main()
{
    ifstream f("lupu.in");
    ofstream g("lupu.out");
    f >> n >> x >> d;
    for(i = 1; i <= n; i ++)
    {
        f >> nr >> val;
        if(val > v[(nr + 1) / d]) v[(nr + 1) / d] = val;
    }
    for(i = 0; i <= x / d; i ++)
        s = s + v[i];
    g << s;
    return 0;
}