#include <fstream>
#define NMAX 5000005

using namespace std;

long long s;
int v[NMAX], deq[NMAX],i,inc,sf,n,k;


int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    f>>n>>k;
    for(i=1;i<=n;i++)
        f>>v[i];
    inc=1;
    sf=0;
    for(i=1;i<=n;i++)
    {
        while((inc<=sf)&&(v[i]<v[deq[sf]]))
            sf--;
        deq[++sf]=i;
        if(deq[inc]==i-k)
            inc++;
        if(i>=k)
            s=s+v[deq[inc]];
    }
    g<<s;
}