#include <fstream>
#include <deque>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");


const int nmax = 5000005;
int n, l;
int a[nmax];

int main(){
    f >> n >> l;
    for(int i = 1; i <= n; i++){
      f >> a[i];
    }
    long long sum = 0;
    deque<int> dq;
    for(int i = 1; i <= n; i++){
      while(!dq.empty() && a[dq.back()] > a[i]){
        dq.pop_back();
      }
      dq.push_back(i);
      if(dq.front() <= i - l){
          dq.pop_front();
      }
      if(i >= l){
         sum += 1ll * a[dq.front()];
      }
       
    }
    g << sum << '\n';
}