#include <fstream>
#include <iostream>
using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");

int main()
{
    long long c[1000005],p[1000005];
    int n,s,t;
    fin >> n >> s >> t;
    t++;
    long long i,m,st=1,dr=0,cost=0;
    for (i=1;i<=n;++i)
    {
        fin >>p[i] >> m;
        if (st <=dr && c[st]==i-t)
            st++;
        while (st<=dr && p[i]<=p[c[dr]]+s*(i-c[dr]))
            dr--;
        c[++dr]=i;
        cost+= m*(p[c[st]]+s*(i-c[st]));
    }
    fout << cost;
    fin.close();
    fout.close();
    return 0;
}