#include <iostream>
#include <stack>
#include <deque>
#include <fstream>
#include <vector>
#include <string>

using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");

int main() {
    deque<int> deq;
    vector<int> p;
    int n,s,t,suma=0;
    fin>>n>>s>>t;
    p.resize(n+1);
    for(int i=1;i<=n;i++)
    {
        int c;
        fin>>p[i]>>c;
        while(!deq.empty()&&i-deq.front()>t)
            deq.pop_front();
        while(!deq.empty()&&(p[deq.back()]+s*(i-deq.back()))>p[i])
            deq.pop_back();
        deq.push_back(i);
        suma+=(s*(i-deq.front())+p[deq.front()])*c;
    }
    fout<<suma;
    return 0;
}