#include <fstream>
#include <deque>
using namespace std;
deque <int> coada;
int v[5000001];
ifstream cin("deque.in");
ofstream cout("deque.out");
int main()
{
    int n, k, i;
    long long s=0;
    cin>>n>>k;
    for( i = 1; i <= n; i++ )
        cin>>v[i];
    coada.push_back(1);
    for( i = 2; i <= k; i++ ){
        while( coada.empty() == false && v[i] < v[coada.back()] )
            coada.pop_back();
        coada.push_back(i);
    }
    s+=v[coada.front()];
    for( i = k + 1; i <= n; i++ ){
        while( coada.empty() == false && v[i] < v[coada.back()] )
            coada.pop_back();
        coada.push_back(i);
        if( coada.front() < i - k + 1 )
            coada.pop_front();
        s+=v[coada.front()];
    }
    cout<<s;
    return 0;
}