n = int(input()) s = input().strip() balloons = 0 solved = set() for char in s: if char not in solved: #balloons += 2 solved.add(char) print(n+len(solved))
n = int(input()) s = input().strip() balloons = 0 solved = set() for char in s: if char not in solved: #balloons += 2 solved.add(char) print(n+len(solved))