#include <fstream>

using namespace std;
ifstream cin("branza.in");
ofstream cout("branza.out");
const int DIM = 5000001;
long long d[DIM], p[DIM], c[DIM];
int main()
{
    int n, s, t;
    cin >> n >> s >> t;

    long long sum = 0;
    int st = 0, dr = -1;
    for(int i = 0; i < n; ++i)
    {
        cin >> p[i] >> c[i];

        if(st <= dr && d[st] == i - t + 1)
        {
            ++st;
        }
        while(st <= dr && p[i] <= p[d[dr]] + s * (i - d[dr]))
        {
            --dr;
        }
        d[++dr] = i;
        sum += c[i] * (p[d[st]] + s * (i - d[st]));
    }

    cout << sum;
    return 0;
}