#include <fstream>
#include <deque>

using namespace std;

ifstream in("branza.in");
ofstream out("branza.out");
pair <int, int> a[100000];
deque <int> dq;

int main()
{
    int n, k, t;
    in >> n >> t >> k;
    long long s = 0;
    for(int i = 0; i < n; i++)
    {
        in >> a[i].first >> a[i].second;
        if(!dq.empty() && dq.front() == i - k)
        {
            dq.pop_front();
        }
        while(!dq.empty() && a[i].first <= a[dq.back()].first + 10 * (i - dq.back()))
        {
            dq.pop_back();
        }
        dq.push_back(i);
        s+=(a[dq.front()].first + 10 * (i - dq.front())) * a[i].second;
    }
    out << s;
    return 0;
}