#include <bits/stdc++.h>

using namespace std;
ifstream r("branza.in");
ofstream w("branza.out");
deque<long long>d;
int v[100002];
int main()
{
    long long n, s, t, c, rez = 0;
    r>>n>>s>>t;
    t++;
    for (int i= 0; i<n; i++)
    {
        r>>v[i]>>c;
        if (d.size()!=0 && d.front()==i-t)
        {
            d.pop_front();
        }
        while (d.size()!=0 && v[d.back()]+(i-d.back())*s>=v[i])
        {
            d.pop_back();
        }
        d.push_back(i);
        rez+=c*(v[d.front()]+(i-d.front())*s);
    }
    w<<rez;
    return 0;
}