function input() {
    var input = document.getElementById("grade").value;
    value = input;
}

function output() {
    value = parseInt(value);

    var grade = "F";
    if (value >= 90)
        grade = "A";
    else if (value >= 80)
        grade = "B";
    else if (value >= 70)
        grade = "C";
    else if (value >= 60)
        grade = "D";
    else
        grade = "F";

    document.writeln(grade);
}