#include <fstream>
#include <deque>

using namespace std;

deque <pair <int, int> > v;
long long s;
int a, n, k;


int main() {
    
    ifstream cin ("deque.in");
    ofstream cout ("deque.out");
    
    cin >> n >> k;
    for (int i=1; i<=k; i++)
    {
        cin >> a;
        while (v.size() > 0 && v.back().first > a )
            v.pop_back();
        v.push_back(make_pair( a, i) );
    }
    s += v.front().first;
    
    for (int i=k+1; i<=n; i++)
    {
        cin >> a;
        if (v.front().second == i-k)
            v.pop_front();
        while (v.size() > 0 && v.back().first > a )
            v.pop_back();
        v.push_back(make_pair( a, i) );
        s += v.front().first;
    }
    
    cout << s;
    
    return 0;
}