#include <fstream>
#define NMAX 5000005

using namespace std;

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

int n, k, a[NMAX], dq[NMAX], in, sf, i;

long long int sum;

int main()
{
    fin>>n>>k;
    for(i=1; i<=n; i++)
        fin>>a[i];

    in=1;
    for(i=1; i<=n; i++)
        {while(in<=sf && a[i]<=a[dq[sf]])
                sf--;
        dq[++sf]=i;
        if(dq[in] == i-k)
            in++;
        if(i>=k)
            sum+=a[dq[in]];
        }

    fout<<sum<<'\n';

    fin.close();
    fout.close();
    return 0;
}