#include <fstream>
using namespace std;
#define maxn 5000010
ifstream f("deque.in");
ofstream g("deque.out");
int N, K;
int A[maxn], Deque[maxn];
int Front, Back;
long long Sum;
int main()
{
    int i;
    f>>N>>K;
    for (i = 1; i <= N; i++)
        f>>A[i];
    Front = 1, Back = 0;
    for (i = 1; i <= N; i++)
    {
        while (Front <= Back && A[i] <= A[ Deque[Back] ]) Back--;
        Deque[++Back] = i;
        if (Deque[Front] == i-K) Front++;
        if (i >= K) Sum += A[ Deque[Front]];
    }
    g<<Sum;
    g.close();
    return 0;
}