#include <cstdio>
#include <deque>

using namespace std;

struct element
{
    int val;
    int poz;
};
deque<element> a;
int s;

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,k;
    element crt;
    scanf("%d%d",&n,&k);
    for(int i=1;i<=n;i++)
    {
        crt.poz=i;
        scanf("%d",&crt.val);
        while(i>1&&a.back().val>=crt.val)
            a.pop_back();
        a.push_back(crt);

        if(a.front().poz<=i-k)
            a.pop_front();
        if(i>=k)
            s+=a.front().val;
    }
    printf("%d\n",s);
    return 0;
}