//Do not declare variable marks.
//Write your code below this line.

arr = [
    [90, 'AA'],
    [80, 'AB'],
    [70, 'BB'],
    [60, 'BC'],
    [50, 'CC'],
    [40, 'CD'],
    [30, 'DD'],
    [-10, 'FF'],
]
    
for(var i = 0; i < arr.length; i++) {
    if(marks > arr[i][0]) {
        console.log(arr[i][1]);
        break;
    }    
}