#include <fstream>
#include <deque>

using namespace std;

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

deque <int> d;

int v[5000005],i,n,k,p,u;
long long s;

int main ()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];
    for(i=1;i<=n;i++)
    {
        while(!d.empty()&&v[i]<v[d[d.size()-1]])
            d.pop_back();
        d.push_back(i);
        if(d[0]==i-k)
            d.pop_front();
        if(i>=k)
            s+=v[d[0]];
    }
    fout<<s;
    return 0;
}