#include <cstdio>
#include <cstdlib>
using namespace std;

#define nmax 5000001

int v[nmax], deque[nmax], front, back, n, k;
long long sum = 0;

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int i;
    scanf("%i %i", &n,&k);
    for(i=1; i<=n; ++i)
    {
                     scanf("%i", &v[i]);
    }
    front = 1;
    back = 0;
    for(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 += v[ deque[front] ];
    }
    printf("%lld\n", sum);
    return 0;
}