fun main(args: Array<String>) {
    val n = readLine()!!.toInt()
    var inputs = mutableListOf<String>()
    for (i in 0..2) {
        var input = readLine()!!
        inputs.add(input)
    }
    var total = 0
    for (i in 0..(n-1)) {
        val a = inputs[0][i]
        val b = inputs[1][i]
        val c = inputs[2][i]

        if (a==b && a==c) {
            continue
        } else if(a==b || a==c || b==c){
            total += 1
        } else {
            total += 2
        }
    }
    print(total)
}