n = int(input())
s = input()
if n == 1:
    print("NO")
elif n == 2:
    if s[0] == s[1]:
        print("YES")
    else:
        print("NO")
elif n == 3:
    if s[0] == s[2] and s[0] != s[1]:
        print("NO")
    else:
        print("YES")
else:
    print("YES")