#include <bits/stdc++.h>

using namespace std;
ifstream f ("branza.in");
ofstream g ("branza.out");

int n,cost,stricat;
deque <pair<int,int>> dq;
int sol;
int main()
{
    f>>n>>cost>>stricat;
    for(int i=1; i<=n; ++i)
    {
        if(!dq.empty() && dq.front().second-i>stricat)
            dq.pop_front();
        int val,it;
        f>>val>>it;
        while(!dq.empty()  &&   (val<(dq.back().first+(i-dq.front().second)*cost   )))
        {
            dq.pop_back();
        }
        dq.push_back({val, i});
        sol+=dq.front().first*it+(i-dq.front().second)*it*cost;

    }
    g<<sol;
    return 0;
}