#include<cstdio>
using namespace std;

int n, k, i;
int v[5000010], Deque[5000010];
int prim, ult;
long long sum;

int main()
    {
        freopen("deque.in","r",stdin);
        freopen("deque.out","w",stdout);
        scanf("%d%d", &n, &k);

        for (i = 1; i <= n; i++)
            scanf("%d", &v[i]);

        prim=1;
        ult=0;

        for(i = 1; i <= n; i++)
        {
            while (prim <= ult && v[i] <= v[ Deque[ult] ])
                ult--;
            Deque[++ult]=i;

            if (Deque[prim] == i - k)
                prim++;
            if (i >= k)
                sum += v[Deque[prim]];
        }

        printf("%lld\n", sum);
    }