#include <bits/stdc++.h>
using namespace std;
struct mutare
 {
     int x1,y1;
 } mut[100001];
int n, m, i, j, k, nr, maxx = -1, l, l1, d, d1, x, c;
long long int s;
bool ok;
vector <int> v;
int main()
{
    ifstream f("lupu.in");
    ofstream g("lupu.out");
    f >> n >> x >> l;
    for(i = 0; i < n; i ++)
    {
        f >> mut[i].x1 >> mut[i].y1;
        m = (x - mut[i].x1) / l + 1;
        if(mut[i].x1 <= x)
        {
            v.push_back(m);
            if(maxx < mut[i].y1) {maxx = mut[i].y1; c = i;}
            ok = true;
        }
    }
    s = s + maxx;
    nr ++;
    v[c] = 0;
    while(ok)
    {
        ok = false;
        maxx = 0;
        for(i = 0; i < v.size(); i ++)
        if(v[i] > nr) {if(maxx < mut[i].y1) {maxx = mut[i].y1; c = i;} ok = true;}
        s = s + maxx;
        nr ++;
        v[c] = 0;
    }
    g << s;
    return 0;
}