fun protectedInput(variableName: String): Int {
    do {
        try {
            print("Enter $variableName: ");
            return readln().toInt();
        } catch (e: Exception) {
            println("${variableName.uppercase()} must be an integer!");
        }
    } while (true)
}

fun main() {
    val n: Int = protectedInput("n");
    val m: Int = protectedInput("m");
    val a: Int = protectedInput("a");
    val b: Int = protectedInput("b");

    val s: Float = (b + m).toFloat() / 2 * (m - b + 1) * (n - a + 1);

    println("S = $s")
}