#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
#define NMAX 5000000
#define VALMAX 10000000
int n,x[NMAX+1],k,minn,s;
int mink(int x[], int pos)
{
    int minn=VALMAX;
    for (int i=pos; i<pos+k; i++)
        minn=min(x[i],minn);
    return minn;
}
int main()
{
    fin >> n >> k;
    for (int i=1; i<=k; i++)
        fin >> x[i];
    minn=mink(x,1);
    s+=minn;
    for (int i=k+1; i<=n; i++)
    {
        fin >> x[i];
        if (x[i-k]==minn)
            minn=mink(x,i-k+1);
        else
            minn=min(minn,x[i]);
        s+=minn;
    }
    fout << s;
    return 0;
}