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

ifstream fin ("branza.in");
ofstream fout ("branza.out");

deque<pair<int, int> >h;
int main()
{
    int n, s, t, rsp=0, c, p, i;
    fin>>n>>s>>t;
    for(i=1; i<=n; i++)
    {
        fin>>c>>p;
        if(!h.empty()&&h.front().second<i-t) h.pop_front();
        while(!h.empty() && c<=h.back().first + s*(i-h.back().second)) h.pop_back();
        h.push_back({c, i});
        rsp += p*(h.front().first + s*(i-h.front().second));
    }
    fout<<rsp;
}