#include <cstdio>
#include <vector>
#include <algorithm>
#include <set>
#define mp make_pair
using namespace std;
vector<pair<int,int> > V;
multiset<int> H;
multiset<int>::iterator it2;
vector<pair<int,int> >::iterator it,lim;
int N, L, K, i, x, cost, Total;
bool cmp(pair<int,int> A, pair<int,int> B)
{
    if (A.second >B.second) return 1;
    return 0;
}
int main()
{
    freopen("lupu.in", "r", stdin);
    freopen("lupu.out", "w", stdout);
    scanf("%d%d%d", &N, &L, &K);
    for (i=1; i<=N; i++)
    {
        scanf("%d%d", &x, &cost);
        V.push_back( mp( cost, (L-x)/K+1 ) );
    }
    sort(V.begin(), V.end(), cmp);
    x=(*V.begin()).second;
    it=V.begin();
    lim=V.end();
    while (x>0)
    {
        while ((*it).second==x && it!=lim)
        {
            H.insert( (*it).first );
            it++;
        }
        it2=H.end();
        it2--;
        Total+=*it2;
        H.erase( it2 );
        x--;
    }
    printf("%d\n", Total);
    return 0;
}