#include <stdio.h>
#include <stdlib.h>

int main() {
    int N, H, U, h[10000],g[10000],i,s=0,j,n,aux,p[10000],x;
    FILE *f1,*f2;
    f1 = fopen ("gutui.in", "r");
    f2 = fopen ("gutui.out", "w");
    fscanf(f1, "%d", &N);
    fscanf(f1, "%d", &H);
    fscanf(f1, "%d", &U);
    for ( i = 0; i < N; i++) {
        fscanf(f1, "%d", &h[i]);
        fscanf(f1, "%d", &g[i]);
    }
    
    for ( i = 0; i < N-1; i++)
        for ( j = i; j < N; j++)
            if (g[i]<g[j]) {
                           aux = g[i];
                           g[i]=g[j];
                           g[j]=aux;
                           aux=h[i];
                           h[i]=h[j];
                           h[j]=aux;}
    n = 1;
    p[0] = H/U - h[0]/U;
    for ( i = 1; i < N; i++){
        x = H/U - h[i]/U;
        for ( j = 0; j < n; j++)
            if (x == p[j]) x--;
        p[i]=x;
        n++;
    }
    
    for ( i = 0; i < N; i++) 
        if (p[i] > 0 ) s=s+g[i];
        
    
    fprintf(f2,"%d",s); 
    fclose(f1);
    fclose(f2);
    
}