#include<iostream>

using namespace std;

void main()
{
	//int x;
	//int y;
	//cout << "Enter two numbers: ";
	////cin >> ignores all leading whitespace
	//// reads until whitespace
	//cout << "a" << endl;
	//cin >> x;
	//cout << "b" << endl;
	//cin >> y;
	//cout << "c" << endl;

	//cout << x  << "+" << y << "=" << x + y << endl;

	//try 2147483647 and 2147483648
	//int bigNumber;
	//cin >> bigNumber;
	//cout << bigNumber << endl;

	float grade;
	cout << "Enter a number grade: ";
	cin >> grade;

	//the if must contain a Boolean expression
	//if(grade >= 90)
	//{
	//	cout << "A" << endl;
	//}
	//if(grade >= 80 && grade < 90)  //(80 <= grade < 90)
	//{
	//	cout << "B" << endl;
	//}
	//if(grade >= 70 && grade < 80) 
	//{
	//	cout << "C" << endl;
	//}
	//if(grade >= 60 && grade < 70) 
	//{
	//	cout << "D" << endl;
	//}
	//if( grade < 60) 
	//{
	//	cout << "F" << endl;
	//}

	//if(grade >= 90)
	//{
	//	cout << "A" << endl;
	//}
	//else
	//{
	//	if(grade >= 80 && grade < 90)  //(80 <= grade < 90)
	//	{
	//		cout << "B" << endl;
	//	}
	//	else
	//	{
	//		if(grade >= 70 && grade < 80) 
	//		{
	//			cout << "C" << endl;
	//		}
	//		else
	//		{
	//			if(grade >= 60 && grade < 70) 
	//			{
	//				cout << "D" << endl;
	//			}
	//			else
	//			{
	//				cout << "F" << endl;
	//			}
	//		}
	//	}
	//}

	if(grade >= 90)
	{
		cout << "A" << endl;
	}
	else if(grade >= 80 && grade < 90)  //(80 <= grade < 90)
	{
		cout << "B" << endl;
	}
	else if(grade >= 70 && grade < 80) 
	{
		cout << "C" << endl;
	}
	else if(grade >= 60 && grade < 70) 
	{
		cout << "D" << endl;
	}
	else 
	{
		cout << "F" << endl;
	}

}