N = int(input())
S = [str(x) for x in input()]

if N == 1:
    print("NO")
elif N == 2:
    if len(set(S)) == 1:
        print("YES")
    else:
        print("NO")
elif N == 3:
    if S[0] == S[1] or S[1] == S[2]:
        print("YES")
    else:
        print("NO")
else:
    print("YES")