#include <iostream>
#include <fstream>
using namespace std;

ifstream f("branza.in");
ofstream g("branza.out");

const int N=1000001;
pair <int,int> v[N];
int d[N];

int main()
{
    int n,t,s1=0,s,st,dr,i;
    f>>n>>s>>t;
    st=0;
    dr=-1;
    for (i=1; i<=n; i++)
    {
        f>>v[i].first;
        f>>v[i].second;
        if ( st <= dr && d[st] == i - t )
            st++;
        while ( st <= dr && v[i].first <= v[d[dr]].first + s * (i - d[dr]) )
            --dr;
        d[++dr]=i;
        s1+=v[i].second * ( v[d[st]] .first+ s*(i-d[st]) );
    }
    g<<s1;
    return 0;
}