using System;

public class Kata
{
  public static char GetGrade(int s1, int s2, int s3)
  {
    int sum = s1 + s2 + s3;
    int avg = (int) (sum / 3.0);

    if (avg >= 90) return 'A';
    else if (avg >= 80) return 'B';
    else if (avg >= 70) return 'C';
    else if (avg >= 60) return 'D';
    else return 'F';
  }
}