#include <fstream>

using namespace std;

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

int n,s,t,st,dr,i,af,c[100005],p[100005],d[100005];

int main()
{
    fin >> n >> s >> t;
    for (i=1;i<=n;i++) fin >> c[i] >> p[i];
    st=dr=1;
    d[1]=1;
    af=c[1]*p[1];
    for (i=2;i<=n;i++)
    {
        while (st<=dr && c[i]<=(i-d[dr])*s+c[d[dr]]) dr--;
        dr++;
        d[dr]=i;
        if (i-t==d[st]+1) st++;
        af+=(c[d[st]]+s*(i-d[st]))*p[i];
    }
    fout << af;

    return 0;
}