#include <bits/stdc++.h>

using namespace std;

ifstream fin("branza.in");
ofstream fout("branza.out");
long long n, s, t, i, j, pr, c[100002];
long long rasp;
deque<long long> q;

int main() {
    fin >> n >> s >> t;

    for(i = 1; i <= n; i++) {
        fin >> c[i] >> pr;
        while(!q.empty() && i - t > q.front()) q.pop_back();
        while(!q.empty() && c[i] < c[q.back()] + (i - q.back()) * s) q.pop_back();
        q.push_back(i);

        rasp += (c[q.front()] + (i - q.front()) * s) * pr;
    }
    fout << rasp;

    return 0;
}