public static void main ( String [ ] $ ) {
  Scanner sc = new Scanner ( in ) ;
  int n = sc . nextInt ( ) , k = sc . nextInt ( ) ;
  long ans = 0 ;
  long [ ] a = new long [ n + 1 ] ;
  for ( int i = 1 ;
  i <= n ;
  i ++ ) {
    a [ i ] = sc . nextLong ( ) ;
    a [ i ] += a [ i - 1 ] ;
  }
  for ( int i = k ;
  i <= n ;
  i ++ ) {
    ans += a [ i ] - a [ i - k ] ;
  }
  out . println ( ans ) ;
}

public static void main ( String [ ] $ ) { Scanner sc = new Scanner ( in ) ; int n = sc . nextInt ( ) , k = sc . nextInt ( ) ; long ans = 0 ; long [ ] a = new long [ n + 1 ] ; for ( int i = 1 ; i <= n ; i ++ ) { a [ i ] = sc . nextLong ( ) ; a [ i ] += a [ i - 1 ] ; } for ( int i = k ; i <= n ; i ++ ) { ans += a [ i ] - a [ i - k ] ; } out . println ( ans ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (array_type element: (type_identifier) dimensions: (dimensions)) name: (identifier))) body: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (type_identifier) arguments: (argument_list (identifier))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (local_variable_declaration type: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (binary_expression left: (identifier) right: (decimal_integer_literal)))))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (identifier)) update: (update_expression (identifier)) body: (block (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))))))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (identifier))) condition: (binary_expression left: (identifier) right: (identifier)) update: (update_expression (identifier)) body: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (identifier)))))))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))))