static int maxSum ( int arr [ ] , int n , int k ) {
  if ( n < k ) {
    return - 1 ;
  }
  int res = 0 ;
  for ( int i = 0 ;
  i < k ;
  i ++ ) res += arr [ i ] ;
  int curr_sum = res ;
  for ( int i = k ;
  i < n ;
  i ++ ) {
    curr_sum += arr [ i ] - arr [ i - k ] ;
    res = Math . max ( res , curr_sum ) ;
  }
  return res ;
}

static int maxSum ( int arr [ ] , int n , int k ) { if ( n < k ) { return - 1 ; } int res = 0 ; for ( int i = 0 ; i < k ; i ++ ) res += arr [ i ] ; int curr_sum = res ; for ( int i = k ; i < n ; i ++ ) { curr_sum += arr [ i ] - arr [ i - k ] ; res = Math . max ( res , curr_sum ) ; } return res ; }
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