#include <fstream>
#define DIM 100002
using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");
long long n, s, t, v[DIM], sol, p, u, i, x[DIM], y[DIM];
int main(){
    f>>n>>s>>t;
    for(i=1; i<=n; i++)
        f>>x[i]>>y[i];
    f.close();
    p=1;
    for(i=1; i<=n; i++)
    {
        while(v[p]+t<i)
            p++;
        while( p<=u && x[i]<= ( x[ v[u] ]+( i-v[u] )*s ) )
            u--;
        v[++u]=i;
        sol+=y[i]*( x[ v[p] ]+( i-v[p] )*s );
    }
    g<<sol<<"\n";
    g.close();
    return 0;
}