#include <fstream>
#include <deque>
using namespace std;
ifstream in ("deque.in");
ofstream out ("deque.out");
deque <long> d;
long  n,i,k,a[50000001];
long long s;
int main()
{
in>>n>>k;
for(i=1;i<=n;i++)in>>a[i];
for(i=1;i<=n;i++)
{
    while(!d.empty()&&a[i]<=a[d.back()])d.pop_back();
    d.push_back(i);
    if(d.front()==i-k){d.pop_front();}
    if(i>=k)s=s+a[d.front()];
}
out<<s;
    return 0;
}