#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
long long a[5000005];
deque<long long>dq;
long long n,k,ans;
int main()
{
    cin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        cin>>a[i];
    }
    for ( int i = 1; i <= k; ++i)
    {
        while(dq.size() > 0 and a[dq.back()] >= a[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
    }
    ans += a[dq.front()];
    for  ( int dr = k+1; dr <= n; ++dr)
    {
        while(dq.size() > 0 and a[dq.back()] >= a[dr])
        {
            dq.pop_back();
        }
        dq.push_back(dr);
        while(dq.size() > 0 and dq.front()<dr-k+1)
        {
            dq.pop_front();
        }
        ans += a[dq.front()];
    }
    cout << ans;
    return 0;
}