#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
long n,i,j,k,v[5000001],d[5000001],st,dr;
long long s;
int main()
{
    f>>n>>k>>v[1];
    d[1]=1;
    dr=1;
    st=1;
    for(i=2;i<=k;i++)
    {
        f>>v[i];
        dr++;
        j=dr-1;
        while (j!=0 && v[i]<=v[d[j]])
            j--;
        dr=j+1;
        d[dr]=i;
    }
    s=v[d[st]];
    for (i=k+1;i<=n;i++)
    {
        f>>v[i];
        if (d[st]<i-k+1)
            st++;
        j=dr;
        while (j>=st && v[i]<=v[d[j]])
            j--;
        dr=j+1;
        d[dr]=i;
        s+=v[d[st]];
    }
    g<<s;
    return 0;
}