#include <fstream>

using namespace std;

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

const int N = 100000;

pair < int, int > v[N];
int d[N];

int main()
{
    int n, s, t, st = 0, dr = -1;
    long long sum = 0;
    cin >> n >> s >> t;
    for (int i = 0; i < n; ++i) {
        cin >> v[i].first >> v[i].second;
        while(st <= dr && d[st] == i - t) {
            ++st;
        }
        while(st <= dr && v[d[dr]].first + s * (i - d[dr]) >= v[i].first) {
            --dr;
        }
        d[++dr] = i;
            sum += (v[d[st]].first + s * (i - d[st])) * v[i].second;
    }
    cout << sum;
    return 0;
}