#include<fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
signed long long sum;
signed long int n,k,a[5000001],b[5000001],st=1,dr=0,i;
int main()
{
    fin>>n>>k;

    for(i=1;i<=n;i++)
        fin>>a[i];
    for(i=1;i<=n;i++)
    {
        while(a[i]<b[dr] && dr>=st)
            dr--;
        b[++dr]=a[i];
        if(i-k>=0)
        {
            if(b[st]==a[i-k])
                st++;
            sum+=b[st];
        }
    }
    fout<<sum;
}