import kotlin.math.min

fun main() {
    readln()
    val old = readln()
    readln().mapIndexed { index, c ->
        when {
            c == old[index] -> 0
            c > old[index] -> min(c - old[index], ('Z' - c) + (old[index] - '@'))
            else -> min(old[index] - c, ('Z' - old[index]) + (c - '@'))
        }
    }.sum().also { println(it) }
}