#include <bits/stdc++.h>
#define n 100005

using namespace std;

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

int main(){
    long long N, S, T, P, C[n], i, s = 0;

    deque<int> d;

    f >> N >> S >> T;

    T++;

    for(i = 0; i < N; i++)
        {
        f >> C[i] >> P;
        if(!d.empty() && d.front() == i - T)
            d.pop_front();

        while(!d.empty() && C[i] <= C[d.back()] + s * (i - d.back()))
            d.pop_back();
        d.push_back(i);
        s += (long long)P * (C[d.front()] + s * (i - d.front()));
        }

    g << s;
}