import Foundation

var count = Int(readLine()!)!
var string = readLine()!
var missing = 0

func checkItHas(_ array: [Character]) -> Bool {
    for a in array {
        if string.contains("\(a)") { return true }
    }
    return false
}

if !checkItHas(Array("abcdefghijklmnopqrstuvwxyz")) { missing += 1}
if !checkItHas(Array("ABCDEFGHIJKLMNOPQRSTUVWXYZ")) { missing += 1}
if !checkItHas(Array("0123456789")) { missing += 1}
if !checkItHas(Array("!@#$%^&*()-+")) { missing += 1}

if count < 6 { print([6-count, missing].max()!)}
else { print(missing) }
// Enter your code here