#include <bits/stdc++.h>
#define MAXN 100000

using namespace std;

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

int pret[MAXN + 1], produs[MAXN + 1];

int main()
{
    int n, s, t, i, afis;

    fin >> n >> s >> t;

    for(i = 1; i <= n; i++){
        fin >> pret[i] >> produs[i];
    }

    deque <int> dq;
    afis = 0;
    for(i = 1; i <= n; i++){
        if(dq.front() == i - t){
            dq.pop_front();
        }
        while(!dq.empty() && pret[i] <= pret[dq.back()] + s * (i - dq.back())){
            dq.pop_back();
        }
        dq.push_back(i);
        afis += produs[i] * (pret[dq.front()] + s * (i - dq.front()));
    }

    fout << afis << "\n";
    return 0;
}