#include <stdio.h>
int a[100000],b[100000];

int main()
{
    FILE *in,*out;
    int jos=0,sus=-1,n,s,t,i;
    long long rez=0;
    in=fopen("branza.in","r");
    out=fopen("branza.out","w");
    fscanf(in,"%d%d%d",&n,&s,&t);
    for(i=0;i<n;i++)
    {
        fscanf(in,"%d%d",&a[++sus],&b[i]);
        while(i-jos+1>t) jos++;
        while(a[sus]<a[jos])  jos++;
        sus=jos;
        rez+=b[i]*a[jos];
        a[jos]+=s;
    }
    fprintf(out,"%lld",rez);
    return 0;
}