public static void main ( String [ ] args ) {
  FastReader fs = new FastReader ( ) ;
  StringBuilder sb = new StringBuilder ( ) ;
  Set < Integer > set = new HashSet < > ( ) ;
  int n = fs . nextInt ( ) ;
  int m = fs . nextInt ( ) ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    String s = fs . next ( ) ;
    int sweet = - 1 ;
    int dwarf = - 1 ;
    for ( int j = 0 ;
    j < m ;
    j ++ ) {
      if ( s . charAt ( j ) == 'G' ) dwarf = j ;
      else if ( s . charAt ( j ) == 'S' ) sweet = j ;
    }
    if ( sweet - dwarf < 0 ) {
      System . out . println ( - 1 ) ;
      return ;
    }
    else set . add ( sweet - dwarf ) ;
  }
  System . out . println ( set . size ( ) ) ;
}

public static void main ( String [ ] args ) { FastReader fs = new FastReader ( ) ; StringBuilder sb = new StringBuilder ( ) ; Set < Integer > set = new HashSet < > ( ) ; int n = fs . nextInt ( ) ; int m = fs . nextInt ( ) ; for ( int i = 0 ; i < n ; i ++ ) { String s = fs . next ( ) ; int sweet = - 1 ; int dwarf = - 1 ; for ( int j = 0 ; j < m ; j ++ ) { if ( s . charAt ( j ) == ' G ' ) dwarf = j ; else if ( s . charAt ( j ) == ' S ' ) sweet = j ; } if ( sweet - dwarf < 0 ) { System . out . println ( - 1 ) ; return ; } else set . add ( sweet - dwarf ) ; } System . out . println ( set . size ( ) ) ; }
(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)))) (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (type_identifier) arguments: (argument_list)))) (local_variable_declaration type: (generic_type (type_identifier) (type_arguments (type_identifier))) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (generic_type (type_identifier) (type_arguments)) arguments: (argument_list)))) (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: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (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 (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: (integral_type) declarator: (variable_declarator name: (identifier) value: (unary_expression operand: (decimal_integer_literal)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (unary_expression operand: (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 (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal))) consequence: (expression_statement (assignment_expression left: (identifier) right: (identifier))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal))) consequence: (expression_statement (assignment_expression left: (identifier) right: (identifier))))))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (identifier)) right: (decimal_integer_literal))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (unary_expression operand: (decimal_integer_literal))))) (return_statement)) alternative: (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (identifier)))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))))