#include <fstream>
#define maxn 5000020
using namespace std;
int v[maxn], Deq[maxn];
int n, i, j, x, st, 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];
    st = 1;
    dr = 0;
    for(i = 1; i <= n; 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;
    return 0;
}