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 f i = if a.[i] = b.[i] && b.[i] = c.[i] then 0 else if a.[i] <> b.[i] && b.[i] <> c.[i] && c.[i] <> a.[i] then 2 else 1
let _ = for i = 0 to n - 1 do ans := !ans + f i done; Printf.printf "%d\n" !ans