#include <iostream>
#include <fstream>

using namespace std;

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

const int N=100000;

long long c[N], nr[N];
int dq[N];

int main()
{
    int n, s, t, st=0, dr=-1;
    long long sum=0;
    in>>n>>s>>t;
    for(int i=0; i<n; i++){
        in>>c[i]>>nr[i];
    }
    for(int i=0; i<n; i++){
        if(st<=dr && dq[st]==i-t){
            st++;
        }
        while(st<=dr && c[i]<=c[dq[dr]]+(i-dq[dr])*s){
            dr--;
        }
        sum+=min(c[i], c[dq[st]]+(i-dq[dr])*s)*nr[i];
        dq[++dr]=i;
    }
    out<<sum;
    return 0;
}