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

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

    seen = set()
    new = [s for s in S]
    for i in range(0, N, 2):
        seen.add(S[i])
        new[i] = ' '
    for i in range(1, N, 2):
        if S[i] in seen:
            new[i] = ' '
    flg = 0
    ok = 0
    for i in range(1, N, 2):
        if flg == 0:
            if new[i] != ' ':
                flg = 1
                ok = 1
                if i == N-1:
                    ok = 0
                    break
        elif flg == 1:
            if new[i] == ' ':
                flg = 2
        elif flg == 2:
            if new[i] != ' ':
                ok = 0
                break
    if ok:
        print('Yes')
        exit()

    seen = set()
    new = [s for s in S]
    for i in range(1, N, 2):
        seen.add(S[i])
        new[i] = ' '
    for i in range(0, N, 2):
        if S[i] in seen:
            new[i] = ' '
    flg = 0
    ok = 0
    for i in range(0, N, 2):
        if flg == 0:
            if new[i] != ' ':
                flg = 1
                ok = 1
                if i == N - 1:
                    ok = 0
                    break
        elif flg == 1:
            if new[i] == ' ':
                flg = 2
        elif flg == 2:
            if new[i] != ' ':
                ok = 0
                break
    if ok:
        print('Yes')
    else:
        print('NO')


if __name__ == '__main__':
    main()