#include <iostream>
#include <fstream>

using namespace std;

const int N = 100001;

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

int n, s, t, c[N], p[N], d[N], dr, st;
long long costul = 0;

int main()
{
    in >> n >> s >> t;
    for (int i=1; i<=n; i++)
    {
        in >> c[i] >> p[i];
    }
    t++;
    st=1;
    dr=0;

    for (int i=1; i<=n; i++)
    {
        if (st <= dr && d[st] == i-t)
        {
            st++;
        }
        while ( st <= dr && c[d[dr]] + s * (i - d[dr]) >= c[i])
        {
            dr--;
        }

        d[++dr]=i;
        costul = costul + (c[d[st]] + (i - d[st]) * (long long)s) * p[i];
    }
    out << costul;
    return 0;
}