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