#include<fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int i;
int a[5000010], deq[5000010];
int n, k, fr, bk;
long long Sum;

int main(){
    fin >> n >> k;
     for (i = 1; i <= n; i++)
        fin >> a[i];

     fr = 1; bk = 0;
     for (i = 1; i <= n; i++){
        while (fr <= bk and a[i] <= a[deq[bk]])
            bk--;
        deq[++bk] = i;
        if (deq[fr] == i - k)
            fr++;
        if (i >= k)
            Sum +=a[deq[fr]];
     }
     fout << Sum;
}