fun main(args: Array<String>) {
    val n = readLine()!!.toInt()
    val a = readLine()!!
    val b = readLine()!!
    val c = readLine()!!
    val count = checkDiff(a, b, c)

    print(count)
}

fun checkDiff(a: String, b: String, c: String): Int {
    var count = 0

    a.forEachIndexed { index: Int, char: Char ->
        val matchAB = char == b[index]
        val matchAC = char == c[index]
        val matchBC = b[index] == c[index]

        val abc = matchAB && matchAC && matchBC
        val ab = matchAB && !matchAC && !matchBC
        val ac = !matchAB && !matchAC && matchBC
        val bc = !matchAB && matchAC && !matchBC

        count += when {
            abc -> 0
            ab -> 1
            ac -> 1
            bc -> 1
            else -> 2
        }
    }

    return count
}