#include <fstream>
#define int long long

using namespace std;

const int NMAX = 1000000;

int v[NMAX + 1], dq[NMAX + 1];

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