#include<stdio.h>
int main()
{
    int N,H,U,i,totalg=0,max1,h[100],g[100];
    FILE * pFile = fopen("gutui.in","r");
    FILE * dFile = fopen("gutui.out","w");
    fscanf(pFile,"%i",&N);
    fscanf(pFile,"%i",&H);
    fscanf(pFile,"%i",&U);
    for(i=0;i<N;i++)
    {
        fscanf(pFile,"%i",&h[i]);
        fscanf(pFile,"%i",&g[i]);
    }
    for(;H>0;H=H-U)
    {
        max1=0;
        for(i=0;i<N;i++)
        {
            if(h[i]<=H)
            {
                if(g[i]>max1);
                {
                    max1=g[i];
                }
            }
        }
        totalg=totalg+max1;
    }
    fprintf(dFile,"%i\n",totalg);
    fclose(pFile);
    fclose(dFile);
    return 0;
}