#include <bits/stdc++.h>
std :: vector <long long int> cost;
std :: deque <int> dq;
long long int ans, p, c, s;
int n, t, i, j;
int main() {
    std :: ios_base :: sync_with_stdio(0);
    dq.push_back(0);
    cost.emplace_back(-1e9);
    std :: ifstream fin("branza.in");
    fin >> n >> s >> t >> c >> p;
    cost.emplace_back(c);
    ans += p * c;
    dq.push_back(1);
    for (i = 2; i <= n; ++ i) {
        fin >> c >> p;
        if (i - dq[1] == t) {
            dq.pop_front();
            dq.front() = 0;
        }
        cost.emplace_back(c);
        while (cost[dq.back()] + (i - dq.back()) * s >= cost[i])
            dq.pop_back();
        dq.push_back(i);
        ans += p * (cost[dq[1]] + (i - dq[1]) * s);
    }
    fin.close();
    std :: ofstream fout("branza.out");
    fout << ans;
    fout.close();
    return 0;
}