#include <fstream>

using namespace std;

const int NMAX = 100005;
long long v[NMAX], dq[NMAX];

int main()
{
    ifstream cin("branza.in");
    ofstream cout("branza.out");
    long long n, t, st = 1, dr = 0, s = 0, k, c;
    cin >> n >> s >> t;
    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;
}