#include <fstream>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,inc=1,sf=0,x,v[500005],c[500005];
long long sum=0;
int main()
{
    fin>>n>>k;
    v[0]=-2000000000;
    for(int i=1;i<=n;i++)
        fin>>v[i];
    for(int i=1;i<=n;i++)
    {
        if(i<k)
        {
            while(v[i]<v[c[sf]]&&inc<=sf)
                sf--;
            sf++;
            c[sf]=i;
        }
        else
        {
            while(c[inc]<(i-k+1)&&inc<=sf)
                inc++;
            while(v[i]<v[c[sf]]&&inc<=sf)
                sf--;
            sf++;
            c[sf]=i;
            sum+=v[c[inc]];
        }
    }
    fout<<sum;

    return 0;
}