#include <stdio.h>
#include <stdlib.h>
int greedy(int c[][2],int n,int h,int u){
	int j,i;
	int m=0,gr=0;
	for (j=h;j>=u;j=j-u) {	
		for (i=0;i<n;i++)
			if(c[i][0]<=j&&c[i][0]>=j-u)
				if(c[i][1]>m) 
					m=c[i][1];
		//printf("%d\n" ,m);
		gr=gr+m;
		m=0;
		}
	return gr;
}
int main(){
	 int c[100000][2];
	 int i,n,h,u;
         freopen("gutui.in", "r", stdin);
         freopen("gutui.out", "w", stdout); 
         scanf("%d",&n);
	 scanf("%d",&h);
	 scanf("%d",&u);
 	 for (i=0;i<n;i++) { 
     	 		scanf("%d",&c[i][0]);
			scanf("%d",&c[i][1]);
	}
	printf("%d",greedy(c,n,h,u));
	return 0;
}