#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

int v[5000000];
deque <int> pos;

int main()
{
    long long sum;
    int n, k, i, x;
    in>>n>>k;
    sum = 0;
    for( i = 1; i <= n; i++ ){
      in>>v[i];
    }

    sum = 0;
    for( i = 1; i <= n; i++ ){
      while( pos.size() > 0 && v[pos.back()] >= v[i] )
        pos.pop_back();

      pos.push_back(i);

      if( pos.front() == i - k){
        //out<<v[pos.front()]<<" "<<pos.size()<<'\n';
        pos.pop_front();
      }
      if( i >= k )
        sum+=v[pos.front()];
    }
    out<<sum;
    return 0;
}