#include <fstream>

using namespace std;

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

long long c[10000000], p;
long long n, s, t, d[100000];

int main()
{
    in >> n >> s >> t;
    t++;
    long long st = 0, dr = -1, sum = 0;
    for(int i = 0; i < n; i++)
    {
        in >> c[i] >> p;
        if(st <= dr && d[st] == i - t)
        {
            st++;
        }
        while(st <= dr && c[i] < c[d[dr]] + (long long)s * (i - d[dr]))
        {
            dr--;
        }
        d[++dr] = i;
        sum += (c[d[st]] + (long long)s * (i - d[st])) * p;
    }
    out << sum << '\n';
    return 0;
}