#include <fstream>
#include <deque>

using namespace std;

ifstream cin("deque.in");
ofstream cout("deque.out");

int n,k,a;

typedef pair<int,int> adat;
deque <adat> x;

int main()
{
    cin>>n>>k;
    int o=0;
    for(int i=1;i<=n;i++)
    {
        cin>>a;

        while(a<=x.back().first && !x.empty())
            x.pop_back();

        x.push_back(adat(a,i));

        while(x.front().second < i-k+1) x.pop_front();

        if(i>=k) o+=x.front().first;

    }

    cout<<o<<"\n";

    return 0;
}