#include <iostream>
#include <fstream>
#define Max 100005
using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");
int v[Max], d[Max],n,s,t;
long long sum;
void rez()
{
    f>>n>>s>>t;
    int head=1,tail=0,i,p;
    for(i=1;i<=n;++i)
    {
        f>>v[i]>>p;
        while(head<=tail&&v[i]<v[d[tail]]+((i-d[tail])*s))tail--;
        d[++tail]=i;
        while(head<=tail&&i-d[head]>=t)head++;
        sum+=(long long)(v[d[head]] +(i-d[head])*s)*p;
    }
    g<<sum;
}
int main()
{
   rez();
    return 0;
}