def main():
    import sys
    input = sys.stdin.readline

    S = input().rstrip('\n')
    N = len(S)

    for i in range(0, N, 2):
        if i == N-1:
            continue
        for j in range(i, N, 2):
            ok = 1
            idx = set()
            for k in range(i, j+1, 2):
                idx.add(k)
            seen = set()
            for k, s in enumerate(S):
                if k not in idx:
                    seen.add(S[k])
            for k in idx:
                if S[k] in seen:
                    ok = 0
                    break
            if ok:
                print('Yes')
                exit()

    for i in range(1, N, 2):
        if i == N-1:
            continue
        for j in range(i, N, 2):
            ok = 1
            idx = set()
            for k in range(i, j+1, 2):
                idx.add(k)
            seen = set()
            for k, s in enumerate(S):
                if k not in idx:
                    seen.add(S[k])
            for k in idx:
                if S[k] in seen:
                    ok = 0
                    break
            if ok:
                print('Yes')
                exit()

    print('NO')


if __name__ == '__main__':
    main()