#include<fstream>
#include<deque>
#define nmax 5000003
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque <long long> deq;
long long i,n,k,x[nmax],s;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>x[i];
    }
    deq.push_front(1);
    for(i=2;i<=k;i++)
    {
        if(x[i]>x[deq.back()])
        deq.push_back(i);
        else
        {
            while(!deq.empty() && x[i]<=x[deq.back()])
            deq.pop_back();
            deq.push_back(i);
        }
    }
    s+=x[deq.front()];
    for(i=k+1;i<=n;i++)
    {
        while(!deq.empty() && x[i]<=x[deq.back()])
        deq.pop_back();
        deq.push_back(i);
        if(deq.front()==i-k)
        deq.pop_front();
        s+=x[deq.front()];
    }
    g<<s;
    return 0;
}