#include <fstream>
using namespace std;

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

long long n,s,t,i,p,u,sol,d[100010],c[100010],P[100010];
int main ()
{

    f>>n>>s>>t;
    for (i=1; i<=n; i++)
        f>>c[i]>>P[i];

    d[1]=1;
    p=1;
    u=1;
    sol+=c[1]*P[1];
    for (i=2; i<=n; i++)
    {
        while (p<=u&&c[i]<=(i-d[u])*s+c[d[u]])
            u--;

        d[++u]=i;
        if (i-d[p]==t+1)
            p++;

        sol+=(c[d[p]]+s*(i-d[p]))*P[i];
    }
    g<<sol;
    return 0;
}