#include <fstream>
#include <deque>
using ll = long long;
#define int ll

using namespace std;

ifstream cin ("branza.in");
ofstream cout ("branza.out");

deque <int> dq;
pair<int, int> v[100005];
int ans[100005];

signed main() {
    int n, s, t;
    cin >> n >> s >> t;
    for(int i = 1; i <= n; i++)
        cin >> v[i].first >> v[i].second;
    int ans = 0;
    for(int i = 1; i <= n; i++) {
        while(!dq.empty() && dq.front() <= i-t)
            dq.pop_front();
        while(!dq.empty() && v[dq.back()].first+(i-dq.back())*s > v[i].first)
            dq.pop_back();
        dq.push_back(i);
        ans += v[i].second*(v[dq.front()].first + (i-dq.front())*s);
    }
    cout << ans;
}