///Deque
///Se da un sir A cu N numere intregi. Pentru fiecare subsecventa de lungime K sa se determine minimul, iar apoi sa se calculeze suma acestor minime.
#include <stdio.h>
#define maxn 5000010

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);
    int i;
    scanf("%d %d ", &N, &K);
    for (i = 1; i <= N; i++)
        scanf("%d ", &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]];
    }
    printf("%lld\n", Sum);
    return 0;
}