#include <fstream>

using namespace std;

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

int f,b,d[5000010],n,i,a[5000010],k;
long long s;

int main()
{


    fin>>n>>k;
    f=1,b=0;
    for(i=1;i<=n;i++)
    {
        fin>>a[i];
    }
    for(i=1;i<=n;i++)
    {
        while(a[d[b]]>a[i] && b>=f)
            b--;
        d[++b]=i;

        if(d[f]==i-k)
            f++;
        if(i>=k)
            s+=a[d[f]];

    }
    fout<<s;


    return 0;
}