#include<fstream>
using namespace std;

struct cell
{
    int cost,cantitate;
};

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

const int NMAX=100005;

int n,s,t;
long long dp[NMAX];
cell a[NMAX];
long long sum;

int main()
{
    int i,j;
    fin>>n>>s>>t;
    for (i=1;i<=n;i++)
        {
            fin>>a[i].cost>>a[i].cantitate;
            dp[i]=1LL*a[i].cost*a[i].cantitate;
            for (j=i-1;j>=1 && j>=i-t;j--)
                dp[i]=min(dp[i],1LL*(i-j)*s*a[i].cantitate+1LL*a[j].cost*a[i].cantitate);
            sum+=dp[i];
        }
    fout<<sum<<"\n";
    return 0;
}