#include <bits/stdc++.h>
#define pii pair < int , int >
using namespace std;
ifstream fin ("lupu.in") ;
ofstream fout ("lupu.out") ;
priority_queue < pii > pq ;
long long answer ;
int n , mx , x , l , k , d , fr[100001] ;
int main ()
{
    fin >> n >> mx >> l ;
    for ( int i = 1 ; i <= n ; i ++ )
    {
        fin >> d >> x ;
        pq.push( make_pair ( x , d ) ) ;
    }
    while ( ! pq.empty() )
    {
        d = pq.top().second ;
        x = pq.top().first ;
        pq.pop() ;
        int k = 0 ;
        while ( fr[k] == 1 && d <= mx )
        {
            d += l ;
            k ++ ;
        }
        if ( fr[k] == 0 && d <= mx )
        {
            fr[k] = 1 ;
            answer += x ;
        }
    }
    fout << answer ;

    return 0 ;
}