#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int deque[5000003],n,k,a[5000003],begin,end;
long long sum;
void read()
{
    f>>n>>k;
    int i;
    for(i=1;i<=n;i++)
        f>>a[i];
}
void calculate()
{
    int i;
    begin=1;end=0;
    for(i=1;i<=k;i++)
        {
            while(begin<=end&&a[i]<=a[deque[end]])
                end--;
            deque[++end]=i;
        }
    sum=a[deque[begin]];
    for(i=k+1;i<=n;i++)
    {
        while(begin<=end&&a[i]<=a[deque[end]])
                end--;
            deque[++end]=i;
        if(deque[begin]==i-k) begin++;
    sum+=a[deque[begin]];
    }
}
void print()
{
    g<<sum<<"\n";
}
int main()
{
    read();
    calculate();
    print();
    return 0;
}