#include <fstream>
#include <queue>

#define f first
#define s second

using namespace std;

ifstream F("lupu.in");
ofstream G("lupu.out");

int n, d, L, x, y, l, maxx;
long long ans;
priority_queue<pair<int, int> > pq;

int main()
{
    F >> n >> d >> L;
    for( int i = 1; i <= n; ++ i )
    {
        F >> x >> y;
        pq.push( { x, y } );
    }
    while( !pq.empty() )
    {
        maxx = 0;
        while( pq.size() && pq.top().f + l + L > d )
        {
            maxx = max( maxx, pq.top().s );
            pq.pop();
        }
        ans += maxx;
        l += L;
    }
    G << ans;
    return 0;
}