#include <fstream>

using namespace std;

const int N = 100000;

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

int v[N], d[N];

int main()
{
    int n, s, t, st, dr, c;
    long long rez = 0;
    in >> n >> s >> t;
    t++;
    st = 0;
    dr = -1;
    for (int i = 0; i < n; i++)
    {
        in >> v[i] >> c;
        if (st <= dr && d[st] == i - t)
        {
            st++;
        }
        while (st <= dr && v[d[dr]] + (i - d[dr])*s >= v[i])
        {
            dr--;
        }
        d[++dr] = i;
        rez += (long long)c * (v[d[st]] + (long long)(i - d[st]) * s);
    }
    out << rez;
    return 0;
}