#include<fstream>
#include<set>
#define a first
#define b second
using namespace std;
ifstream fin("lupu.in");
ofstream fout("lupu.out");
int n,x,l,in,r,b[100005],ma;
pair<int,int >v[100005];
int main()
{
    fin>>n>>x>>l;
    for(int i=1;i<=n;i++)
        fin>>v[i].a>>v[i].b;
    for(int i=0;i<=x;i+=l)
    {
        ma=-1;
        int c=0;
        for(int j=1;j<=n;j++)
            if(v[j].a<=i&&v[j].b>ma&&b[j]==0)
            {
                ma=v[j].b;
                c=j;
            }
        if(ma!=-1)
            r+=ma;
        b[c]=1;
    }
    fout<<r;
}