Letter Grade

Convert a numeric grade to a letter grade:

• A for grades from 90 to 100
• B for grades from 80 to 89
• C for grades from 70 to 79
• D for grades from 60 to 69
• F for grades lower than 60

Input

An integer that represents the grade.

Output

Print the corresponding letter.

Examples

Input:

85

Output:

B