#include <iostream>
#include <fstream>
using namespace std;
int c[1000000], v[1000000], d[1000000];

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

    return 0;
}