#include <iostream>
#include <fstream>
#include <cstdlib>
#include <ctime>
#include <deque>

using namespace std;
ifstream in("branza.in");
ofstream out("branza.out");

#define ll long long
#define ull unsigned long long
#define ui unsigned int
#define pb push_back
const int NMax = 5e5 + 5;
const int strMax = 7*NMax + 50;
const short inf = 31e3 + 5;

int N,S,T;

struct elem {
    int idx,val;
    elem(int _idx = 0,int _val = 0) {
        idx = _idx;
        val = _val;
    }
};
deque<elem> deq;
// idx - indexul saptamanii respective din deque;
// val - costul pentru a produce un kg de branza in saptamana idx;

int main() {
    in>>N>>S>>T;

    ll ans = 0;
    for (int i=1;i <= N;++i) {
        int C,P;
        in>>C>>P;

        // in fiecare zi ai de ales intre a produce branza azi
        // si a folosi branza care s-ar fi putut produce intr-una din ultimele T saptamani;
        // minimul se obtine cu ajutorul unui deque;
        while (deq.size() && deq.back().val + (i-deq.back().idx)*S >= C) {
            deq.pop_back();
        }
        deq.push_back(elem(i,C));
        if (deq.front().idx == i-T-1) {
            deq.pop_front();
        }

        // deq.front() va reprezenta alegerea optima pentru ziua i;

        ans += 1LL * deq.front().val * P + 1LL * (i-deq.front().idx) * S * P;
    }

    out<<ans<<'\n';

    in.close();out.close();
    return 0;
}