#include <fstream>

using namespace std;

long long v[100001], dq[100001];

int main()
{
    ifstream cin("branza.in");
    ofstream cout("branza.out");
    long long s = 0, n, t, st, dr, i, p;
    cin >> n >> s >> t;
    st = 0;
    dr = -1;
    for (i = 0; i < n; i++)
    {
        cin >> v[i] >> p;
        if (st <= dr && d[st] == i - t - 1)
            st++;
        while (st <= dr && v[i] <= v[d[dr]] + s * (i - d[dr]))
            dr--;
        d[++dr] = i;
        s += p * (v[d[st]] + s * (i - d[st]));
    }
    cout << s;
    return 0;
}