#include <fstream>

using namespace std;

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

int const N=100001;
int d[N], c[N];

int main()
{
    int n, s, t, st=0, dr=-1, p, sum=0;
    in>>n>>s>>t;
    t++;
    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]]+s*(i-d[dr])) dr--;
        d[++dr]=i;
        sum+=p*(c[d[st]]+s*(i-d[st]));
    }
    out<<sum;
    return 0;
}