#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
long long v [ 5000005 ];
int main()
{
    long long n, k ;
    deque<int> dq ;
    cin >> n >> k ;
    for ( int i = 1; i <= k ; i ++ )
    {
        cin >> v[ i ] ;

        while ( !dq.empty() && v[dq.back()] >= v [ i ] )
            dq.pop_back();

        dq.push_front( i ) ;

    }



    long long sum = 0 ;
    sum += v[dq.back()];
;

    for ( int i = k + 1 ; i <= n ; i ++ )
    {
        cin >> v[ i ];

        while (!dq.empty() &&  i - k + 1 > dq.back() )
        {
            dq.pop_back();
        }

        while ( !dq.empty() && v[dq.back()] >= v [ i ] )
            dq.pop_back();

        dq.push_front( i );

        sum += v[dq.back()];


    }
    cout << sum ;
    return 0;
}