#include <bits/stdc++.h>
#include <deque>
using namespace std;

ifstream in("branza.in");
ofstream out("branza.out");
int v[100005];
int dequeMin[100005];
int kg[100005];

int main()
{
    int n, k,s;
    int sum = 0;
    in >> n >> s >> k;



    for (int i = 1; i <= n; i++)
    {
        in >> v[i]>> kg[i];
    }

    int front= 1, back= 0;


	for (int i = 1; i <= n; i++)
    {   

        while(front <= back && v[i] - s*(back-front +1) < v[dequeMin[front]])
            front++;

        back++;
        dequeMin[back]=i;
        if (dequeMin[front] == i-k) front++;

        sum += kg[i] * v[dequeMin[front]];

        for (size_t j = front +1; j <= back; j++)
        {
            sum += kg[dequeMin[back]]*s;
        }
        
    }

    out << sum;

	return 0;
}