fun main(args: Array<String>) {
    val n = Integer.parseInt(readInputLine())
    val a = readInputLine().toCharArray()
    val b = readInputLine().toCharArray()
    val c = readInputLine().toCharArray()
    
    var ans = 0
    
    for (i in 0 until n) {
        ans += setOf<Char>(a[i], b[i], c[i]).count() - 1
    }
    
    println(ans)
}
 
fun readInputLine(): String {
    return readLine()!!
}
