#include <iostream>
#include <bits/stdc++.h>
#include <fstream>
using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");
int N,S,T;
int C[100010],P[100010];
deque<int> dq;
int main()
{
    fin >> N >> S >> T;
    long long int suma = 0;
    for(int i = 1; i <=N; i++){
        fin >> C[i] >> P[i];
    };
    for(int i = 1; i <=N; i++){
        if(!dq.empty() && dq.front() == i-T-1){
            dq.pop_front();
        };
        while(!dq.empty() && C[i] <= (C[dq.back()] +(i-dq.back())*S)){
            dq.pop_back();
        };
        dq.push_back(i);
        suma += (long long)(P[i]*(long long)(C[dq.front()] + S*(i-dq.front())));
    };
    fout << suma;
    return 0;
}