#include <cstdio>
#define NMAX 500002
using namespace std;

int n, k, V[NMAX], Deque[NMAX];
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", &V[i]);

    Front=1;Back=0;
    for(int i=1; i<=n; i++)
    {
        while(Front<=Back&&V[i]<=V[Deque[Back]]) Back--;

        Deque[++Back]=i;

        if(Deque[Front]==i-k) Front++;

        if(i>=k)
            Sum=Sum+V[Deque[Front]];
    }
    printf("%d\n", Sum);
    return 0;
}