#include <stdio.h>
#define maxn 5000010

using namespace std;

int N, K;
int A[maxn], Deque[maxn];
int Front, Back;
long long Sum;

int main() {
    freopen ("deque.in", "r", stdin);
    freopen ("deque.out", "w", stdout);
    scanf ("%d %d", &N, &K);
    for (int i = 1; i <= N; ++i)
        scanf ("%d", &A[i]);
    Front = 1;
    Back = 0;
    for (int 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]];
    }
    printf("%lld\n", Sum);
    return 0;
}