#include <fstream>
#include <iostream>

using namespace std;

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

const int N = 100001;
int cost[N], nr[N], dq[N];

int main()
{
    int n, s, t;
    in >> n >> s >> t;
    t++;
    for(int i=0; i<n; i++) in >> cost[i] >> nr[i];

    int st=0, dr=-1;
    long long rez=0;
    for(int i=0; i<n; i++)
    {
        if(st<=dr && dq[st]==i-t)
            st++;

        while(st<=dr && cost[i]*nr[i]<=(cost[dq[st]]+(i-dq[st])*s)*nr[i])
            st++;

        dq[++dr]=i;

        rez+=(cost[dq[st]]+(i-dq[st])*s)*nr[i];
    }
    out << rez;
    return 0;
}