#include <iostream>
#include <fstream>
#include <cmath>
#include <deque>

using namespace std;

int k;
long long n, t, x, y, i, s;
deque <long long> deque1, deque2;

int main()
{
	ifstream in("branza.in");
	ofstream out("branza.out");

	in>>n>>k>>t;

    for(i = 1; i <= n; i++)
    {
        in>>x>>y;
        while(i - deque2.front() > t && deque1.size() != 0)
        {
            deque1.pop_front();
            deque2.pop_front();
        }
        if(deque1.size() == 0)
        {
            s += x * y;
            deque1.push_back(x);
            deque2.push_back(i);
        }
            else{
                if(x * y <= y * deque1.back() + k * (i - deque2.back()) * y)
                    {
                        s += x * y;
                        deque1.push_back(x);
                        deque2.push_back(i);
                    }
                   else
                        s = s + y * deque1.back() + k * (i - deque2.back()) * y;
            }
    }
	out<<s;
	return 0;
}