let n, a, b, c = Scanf.scanf " %d %s %s %s" @@ fun a b c d -> a, b, c, d
let ans = ref 0
let _ = String.iteri (fun i x -> ans := !ans + List.(length @@ sort_uniq compare [x; b.[i]; c.[i]]) - 1) a; Printf.printf "%d\n" !ans