#include <fstream>
#include <deque>

using namespace std;

const int MAX = 5000005;

int N, K, V[MAX];
long long Ans;

deque<int> Dq;

int main() {
    ifstream in("deque.in");
    in >> N >> K;
    for(int i = 1; i <= N; i++) {
        in >> V[i];
        while(!Dq.empty() && V[Dq.back()] >= V[i])
            Dq.pop_back();
        Dq.push_back(i);
        while(Dq.front() <= i - K)
            Dq.pop_front();
        if(i >= K) 
            Ans += V[Dq.front()];
    } in.close();
    ofstream out("deque.out");
    out << Ans << "\n";
}