#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n, k;
long long sum;
deque < pair <int, int> > dq;
int main() {
    f>>n>>k;
    for (int x, i=1; i<=k; i++) {
        f>>x;
        if (dq.empty()){
            dq.push_back(make_pair(x, i));
        }
        else {
            while (!dq.empty() && dq.back().first>x){
                dq.pop_back();
            }
            dq.push_back(make_pair(x, i));
        }
    }
    sum+=dq.front().first;
    for (int x, i=k+1; i<=n; i++) {
        f>>x;
        if (dq.front().second<=i-k){
            dq.pop_front();
        }
        if (dq.empty()){
            dq.push_back(make_pair(x, i));
        }
        else {
            while (!dq.empty() && dq.back().first>x){
                dq.pop_back();
            }
            dq.push_back(make_pair(x, i));
        }
        sum=1LL*sum+dq.front().first;
    }
    g<<sum;
    return 0;
}