#include <fstream>
#include <deque>
using namespace std;

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

int n, k;
deque<int> d;
int a[5000001];
long long suma;

int main()
{
    fin >> n >> k;
    for( int i = 1; i <= n; ++i )
        fin >> a[i];
    for( int i = 1; i <= n; ++i )
    {
        while( !d.empty() && a[i] <= a[d.back()] )
            d.pop_back();
        d.push_back( i );
        if( i - k == d.front() )
            d.pop_front();
        if( i >= k )
            suma += a[d.front()];
    }
    fout << suma << '\n';
    fin.close();
    fout.close();
    return 0;
}