#include <bits/stdc++.h>

using namespace std;

ifstream f("branza.in");
ofstream g("branza.out");

long long c[100005];
int main(){
    long long n, s, t, p, i, suma = 0;
    deque<int> deq;

    f >> n >> s >> t;

    t++;

    for(i = 0; i < n; i++)
        {
        f >> c[i] >> p;
        if(!deq.empty() && deq.front() == i - t)
            deq.pop_front();
        while(!deq.empty() && c[i] <= c[deq.back()] + s * (i - deq.back()))
            deq.pop_back();
        deq.push_back(i);
        suma = suma + p * (c[deq.front()] + s * (i - deq.front()));
        }
    g << suma;
}