#include <iostream>
#include <fstream>
#include <queue>
using namespace std;
ifstream fin("lupu.in");
ofstream fout("lupu.out");
struct Sheep
{
    bool operator()( pair < int, int > A,  pair < int, int > B)
    {
       if(A.first != B.first)
        return A.first < B.first;
       else
        return A.second > B.second;
    }
};
priority_queue < int, vector < pair < int, int > >, Sheep > Q;
int N, L, D;
void Read()
{
    fin >> N >> L >> D;
    for(int i = 1; i <= N; ++ i)
    {
        int A, B;
        fin >> A >> B;
        Q.push(make_pair(B, A));
    }
}
void Task()
{
    int R = D;
    long long SUM = 0;
    SUM += Q.top().first;
    Q.pop();
    while(!Q.empty())
    {
       if(Q.top().second + D <= L)
       {
           D += R;
           SUM += Q.top().first;
       }
       Q.pop();
    }
    fout << SUM;
}
int main()
{
    Read();
    Task();
    return 0;
}