import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1

def main():
    ss = input().split(" ")
    for s in ss:
        if len(s) == 1 and ord("a") <= ord(s) <= ord("z"): continue
        print("No")
        exit()
    print("Yes")

main()