#include <fstream>
#include <deque>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");

int main() {
    int n,k,a;
    long long int suma=0;
    deque < pair<int,int> > d;
    in>>n>>k;
     for(int i=1;i<=k;i++)
     {
         in>>a;
        while(!d.empty() && a<=d.back().first)
            d.pop_back();
        d.push_back(make_pair(a,i)); 
     }
            suma=suma+d.front().first;

    for(int i=k+1;i<=n;i++)
    {
        in>>a;
          while(!d.empty() && a<=d.back().first)
            d.pop_back();
        d.push_back(make_pair(a,i)); 
        
        if(d.front().second<=i-k)
            d.pop_front();
        
        suma=suma+d.front().first;
    }
    out<<suma;
    return 0;
}