#include <fstream>
#define maxn 5000020
using namespace std;
int v[maxn], Deq[maxn], n, i, x, st = 1, dr, k;
long long s;
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    f >> n >> k;
    for(i = 1; i <= n; ++ i)
    {
        f >> v[i];
        while(st <= dr && v[i] <= v[Deq[dr]]) dr --;
        Deq[++ dr] = i;
        while(Deq[st] <= i - k) st ++;
        if(i >= k) s = s + v[Deq[st]];
    }
    g << s;
    f.close();
    g.close();
    return 0;
}