#include <fstream>
#define nmax 100005

using namespace std;

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

long long n, t, s, a;

long long d[nmax], v[nmax], p=1, q;

long long sum;

int main()
{
    in>>n>>s>>t;
    for(int i=1; i<=n; i++)
    {
        in>>v[i]>>a;
        if(i-d[p] > t)
            p++;
        while(v[i]<= v[d[q]] + s*(i-d[q]) && q>=p)
        {
            q--;
        }
        q++;
        d[q]=i;
        sum += a*(s*(i-d[p])+v[d[p]]);
    }
    out<<sum;
    return 0;
}