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

using namespace std;
#define maxn 300005

int n, k, i, s, x, y, t;
int a[maxn];
deque <int> 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;
        if(deque1.size() != 0){
            if(i - deque2.back() >= t)
            {
                s += x * y;
                deque1.push_back(x);
                deque2.push_back(i);
            }
            else {
                if(x - deque1.back() < k)
                {
                    s += x * y;
                    deque1.push_back(x);
                    deque2.push_back(i);
                }
                    else{
                        s += y * deque1.back() + k * (i - deque2.back()) * y;
                    }
            }
        }
            else{
                s += x * y;
                deque1.push_back(x);
                deque2.push_back(i);
        }


    }
	out<<s;
	return 0;
}