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

int main()
{
    ifstream cin("branza.in");
    ofstream cout("branza.out");
    int n, s, t;
    cin >> n >> s >> t;
    long long cost_minim=0; //costul minim necesar cerut de problema
    deque<pair<int, int>> minime; //deque cu indicii saptamanilor cu costul minim pe prima pozitie si aceste costuri pe a doua pozitie
    for(int i=0; i<n; i++)
    {
        int c, p;
        cin >> c >> p;
        while(!minime.empty() && (minime.back().second)+(i-minime.back().first)*s>=c)
        {
            minime.pop_back();
        }
        pair<int, int> cost; //costul din saptamana i
        cost.first=i; cost.second=c;
        minime.push_back(cost);
        if(minime.front().first<i-t)
        {
            minime.pop_front();
        }
        cost_minim+=(minime.front().second+(i-minime.front().first)*s)*p;
    }
    cout << cost_minim;

    return 0;
}