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

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

const int N = 1e5+5;
long long rez;
int n, i, s, T;
int c[N], p[N];
deque <int> deq;

int main()
{
    fin >> n >> s >> T;
    for(i = 1; i <= n; i++)
        fin >> c[i] >> p[i];
    for(i = 1; i <= n; i++){
        while(!deq.empty() && c[i] * p[i] <= (c[deq.back()] + s) * p[i])
            deq.pop_back();

        deq.push_back(i);

        if(i - deq.front() == T)
            deq.pop_front();

        rez += (c[deq.front()] + s * (i - deq.front())) * p[i];

    }
    fout << rez;
    return 0;
}