#include <fstream>
#include<iostream>

using namespace std;

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

int n,t, s, a[100001], dq[100001], st, dr, p;

void stanga( int i )
{
    if ( dq[st] == i - t )
        st++;
}

void dreapta( int i )
{
    while( st <= dr && a[i] < a[ dq[dr] ] + s * ( i - dq[dr] ) )
        dr--;
    dq[++dr] = i;
}

int main()
{
    in >> n >> s >> t;
    int i;
    long long nr = 0;
    in >> a[1] >> p;
    dq[st] = 1;
    dq[dr] = 1;
    nr = a[1] * p;
    for ( i = 2; i <= n; i++ )
    {
        in >> a[i] >> p;
        stanga(i);
        dreapta(i);
        nr += a[ dq[st] ] * p + s * p * ( i - dq[st] );
    }
    out << nr;
    return 0;
}