#include <iostream>
#include<cstdio>
using namespace std;
const int N=100001;
int v[N],d[N],buc[N];
int main()
{
    int n,s,t,dr=0,st=1,i;
    FILE*fin,*fout;
    fin=fopen("branza.in","r");
    fout=fopen("branza.out","w");
    fscanf(fin,"%d%d%d",&n,&s,&t);
    t--;
    for(i=1;i<=n;i++){
      fscanf(fin,"%d%d",&v[i],&buc[i]);
    }
    long long sum=0;
    for(i=1;i<=n;i++){
      while(st<=dr && v[i]<=s*(i-d[dr])+v[d[dr]])
        dr--;
      d[++dr]=i;
      while(dr-st+1>t){
        st++;
      }
      sum+=(long long)buc[i]*(s*(i-d[st])+v[d[st]]);
    }
    fprintf(fout,"%lld",sum);

    return 0;
}