#include <bits/stdc++.h>
#define FOR(NUM) for(int i = 1; i <= n; ++ i)
using namespace std;

ifstream fin("lupu.in");
ofstream fout("lupu.out");

struct oaie
{
    int dist, cost;
};

int n, distanta, sigma;
vector<pair<int,int>>v;

inline void solve()
{
    sort(v.begin(), v.end());
    int i = 0, new_interval = v[0].first, ans = 0;
    while(i < n)
    {
        int maxi = INT_MIN;
        while(v[i].first == new_interval)
        {
            maxi = max(v[i].second, maxi);
            i++;
        }
        new_interval = v[i].first;
        ans += maxi;
    }
    fout << ans;
}

int main()
{
    fin >> n >> distanta >> sigma;
    FOR(n)
    {
        int x, y;
        fin >> x >> y;
        v.push_back({((distanta - x) / sigma) + 1, y});
    }
    solve();
}