#include <fstream>
#include <deque>
#define MAXN 5000000
using namespace std;

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

deque <int> d;
int v[MAXN + 1];

int main(){
  int n, k, i;
  long long s;
  fin >> n >> k;
  s = 0;
  for( i = 0; i < n; i++ ){
    fin >> v[i];
    if( !d.empty() && d.front() == i - k )
      d.pop_front();
    while( !d.empty() && v[d.back()] >= v[i] )
      d.pop_back();
    d.push_back(i);
    if( i >= k - 1 )
      s += v[d.front()];
  }
  fout << s;
  return 0;
}