S = input().strip()
unique_letters = set(c for c in S if c != ' ')
found = False

# Precompute all possible subsets of unique letters using bitmask
from itertools import chain, combinations

def all_subsets(s):
    return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))

for subset in all_subsets(unique_letters):
    R = set(subset)
    transformed = []
    for c in S:
        if c == ' ':
            transformed.append(' ')
        elif c in R:
            transformed.append(c)
        else:
            transformed.append(' ')
    # Trim leading and trailing spaces
    s = ''.join(transformed).strip()
    if len(s) < 2:
        continue
    # Check all even positions (1-based) are spaces and odd are letters
    valid = True
    for i in range(len(s)):
        if (i+1) % 2 == 1:  # odd positions must be letters
            if s[i] == ' ':
                valid = False
                break
        else:  # even positions must be spaces
            if s[i] != ' ':
                valid = False
                break
    if valid:
        found = True
        break

print("Yes" if found else "NO")