#pragma GCC optimize ( "O3" )
#pragma GCC target ( "avx" )
#include <bits/stdc++.h>
using namespace std;

using ll = long long;

#define TYPE_OF( VAR ) remove_const<remove_reference<decltype( VAR )>::type >::type
#define UNTIE ios_base::sync_with_stdio( false ); cin.tie( nullptr ) 
#define CEXPR( LL , BOUND , VALUE ) constexpr const LL BOUND = VALUE 
#define CIN( LL , A ) LL A; cin >> A 
#define ASSERT( A , MIN , MAX ) assert( MIN <= A && A <= MAX ) 
#define CIN_ASSERT( A , MIN , MAX ) CIN( TYPE_OF( MAX ) , A ); ASSERT( A , MIN , MAX ) 
#define FOR( VAR , INITIAL , FINAL_PLUS_ONE ) for( TYPE_OF( FINAL_PLUS_ONE ) VAR = INITIAL ; VAR < FINAL_PLUS_ONE ; VAR ++ ) 
#define FOREQ( VAR , INITIAL , FINAL ) for( TYPE_OF( FINAL ) VAR = INITIAL ; VAR <= FINAL ; VAR ++ ) 
#define QUIT return 0 
#define RETURN( ANSWER ) cout << ( ANSWER ) << "\n"; QUIT 

#define UPDATE					\
  ll& dp_curr = dp[i];				\
  dp_curr = dp_min + Ai;			\
  if( dp_min < dp_curr ){			\
    if( dp_min == dp[i - K] ){			\
      dp_min = dp_curr;				\
      FOR( j , i - K + 1 , i ){			\
	const ll& dp_j = dp[j];			\
	if( dp_min > dp_j ){			\
	  dp_min = dp_j;			\
	}					\
      }						\
    }						\
  } else if( dp_min  > dp_curr ){		\
    dp_min = dp_curr;				\
  }						\
						\


int main()
{
  UNTIE;
  // CEXPR( int , bound_N , 200000 );
  CEXPR( int , bound_N , 20 );
  CIN_ASSERT( N , 2 , bound_N );
  CIN_ASSERT( K , 2 , N );
  ll dp[bound_N + 2];
  dp[0] = 0;
  ll sum = 0;
  CEXPR( int , bound_Ai , 1000000000 );
  FOR( i , 1 , K ){
    CIN_ASSERT( Ai , 1 , bound_Ai );
    dp[i] = Ai;
    sum += Ai;
  }
  ll dp_min = 0;
  FOREQ( i , K , N ){
    CIN_ASSERT( Ai , 1 , bound_Ai );
    UPDATE;
    sum += Ai;
  }
  RETURN( sum - dp_min );
}