public static void main ( String [ ] args ) {
  Scanner scanner = new Scanner ( System . in ) ;
  int N = scanner . nextInt ( ) ;
  String S = scanner . next ( ) ;
  boolean flag = true ;
  if ( N % 2 == 0 ) {
    flag = false ;
  }
  if ( N % 2 != 0 ) {
    for ( int i = 0 ;
    i < S . length ( ) ;
    i ++ ) {
      if ( N % 3 == 1 ) {
        if ( i % 3 == 0 && S . charAt ( i ) != 'b' ) {
          flag = false ;
        }
        else if ( i % 3 == 1 && S . charAt ( i ) != 'c' ) {
          flag = false ;
        }
        else if ( i % 3 == 2 && S . charAt ( i ) != 'a' ) {
          flag = false ;
        }
      }
      if ( N % 3 == 0 ) {
        if ( i % 3 == 0 && S . charAt ( i ) != 'a' ) {
          flag = false ;
        }
        else if ( i % 3 == 1 && S . charAt ( i ) != 'b' ) {
          flag = false ;
        }
        else if ( i % 3 == 2 && S . charAt ( i ) != 'c' ) {
          flag = false ;
        }
      }
      if ( N % 3 == 2 ) {
        if ( i % 3 == 0 && S . charAt ( i ) != 'c' ) {
          flag = false ;
        }
        else if ( i % 3 == 1 && S . charAt ( i ) != 'a' ) {
          flag = false ;
        }
        else if ( i % 3 == 2 && S . charAt ( i ) != 'b' ) {
          flag = false ;
        }
      }
    }
  }
  if ( flag == true ) {
    System . out . println ( S . length ( ) / 2 ) ;
  }
  else if ( flag == false ) {
    System . out . println ( - 1 ) ;
  }
}

public static void main ( String [ ] args ) { Scanner scanner = new Scanner ( System . in ) ; int N = scanner . nextInt ( ) ; String S = scanner . next ( ) ; boolean flag = true ; if ( N % 2 == 0 ) { flag = false ; } if ( N % 2 != 0 ) { for ( int i = 0 ; i < S . length ( ) ; i ++ ) { if ( N % 3 == 1 ) { if ( i % 3 == 0 && S . charAt ( i ) != ' b ' ) { flag = false ; } else if ( i % 3 == 1 && S . charAt ( i ) != ' c ' ) { flag = false ; } else if ( i % 3 == 2 && S . charAt ( i ) != ' a ' ) { flag = false ; } } if ( N % 3 == 0 ) { if ( i % 3 == 0 && S . charAt ( i ) != ' a ' ) { flag = false ; } else if ( i % 3 == 1 && S . charAt ( i ) != ' b ' ) { flag = false ; } else if ( i % 3 == 2 && S . charAt ( i ) != ' c ' ) { flag = false ; } } if ( N % 3 == 2 ) { if ( i % 3 == 0 && S . charAt ( i ) != ' c ' ) { flag = false ; } else if ( i % 3 == 1 && S . charAt ( i ) != ' a ' ) { flag = false ; } else if ( i % 3 == 2 && S . charAt ( i ) != ' b ' ) { flag = false ; } } } } if ( flag == true ) { System . out . println ( S . length ( ) / 2 ) ; } else if ( flag == false ) { System . out . println ( - 1 ) ; } }
(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 (field_access object: (identifier) field: (identifier)))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (boolean_type) declarator: (variable_declarator name: (identifier) value: (true))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (false))))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (false)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (false)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (false))))))))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (false)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (false)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (false))))))))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (false)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (false)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (false))))))))))))) (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (true))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (decimal_integer_literal)))))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (false))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (unary_expression operand: (decimal_integer_literal))))))))))