#include <fstream>
#include <deque>
#include <limits.h>
#define ll long long
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque< pair<ll,int> > q;
int n,k;
ll a,suma;
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(NULL);
    cin>>n>>k;
    cin>>a;
    q.push_back(make_pair(a,1));
    for(int i=2; i<=k; ++i)
    {
        cin>>a;
        while(a<=q.back().first&&q.size()) q.pop_back();
        q.push_back(make_pair(a,i));
    }
    suma+=q.front().first;
    for(int i=k+1; i<=n; ++i)
    {
        cin>>a;
        while(q.front().second<=i-k&&q.size()) q.pop_front();
        while(a<=q.back().first&&q.size()) q.pop_back();
        q.push_back(make_pair(a,i));
        suma+=q.front().first;
    }
    cout<<suma<<"\n";
    return 0;
}