//horatiu11
# include <cstdio>
# include <deque>
using namespace std;
int n,k,a[5000001];
long long s;
deque <int>d;
int main()
{
    int i;
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;++i)
    {
        scanf("%d",&a[i]);
        while(!d.empty() && a[d.back()]>a[i])
            d.pop_back();
        d.push_back(i);
        if(d.front()== i-k)
            d.pop_front();
        if(i>=k && !d.empty())s+=a[d.front()];
    }
    printf("%lld\n",s);
    return 0;
}