#include <fstream>
#include <queue>

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