#include <bits/stdc++.h>

using namespace std;
ifstream in("branza.in");
ofstream out("branza.out");
int main()
{
    int n,s,t;
    in>>n>>s>>t;
    vector<int> cost(n);
    long long cost_total=0;
    t++;
    deque <int> dq;
    for(int i=0;i<n;i++)
    {
        int cantitate;
        in >> cost[i] >> cantitate;
        if(!dq.empty()&&dq.front()==i-t)
            dq.pop_front();
        while(!dq.empty()&&cost[i]<=cost[dq.back()]+(i-dq.back())*s)
            dq.pop_back();
        dq.push_back(i);
        cost_total+=(long long) cantitate*(cost[dq.front()]+(i-dq.front())*s);
    }
    out<<cost_total;
    return 0;
}