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

using namespace std;

int k;
long long n, t, x, y, i, s, mini;
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{
                deque<long long>::iterator it1 = deque1.begin();
                deque<long long>::iterator it2 = deque2.begin();
                mini = x * y;
                while(it1 != deque1.end())
                   {
                       if(((*it1) * y + k * y * (i - (*it2))) < mini) mini = (*it1) * y + k * y * (i - (*it2));
                       *it2++;
                       *it1++;
                   }
                s += mini;
                deque1.push_back(x);
                deque2.push_back(i);
            }
    }
	out<<s;
	return 0;
}