s=input()
n=len(s)
if n==1:
    print("NO")
    exit()
ok=0
for i in range(n-1):
    for j in range(i, n):
        if (j-i)%2==1:
            continue
        b=0
        dame=0
        for k in range(i, j+1):
            if (k-i)%2==0:
                if s[k]==' ':
                    dame=1
                    break
                if ord(s[k])-ord("a")<0:
                    continue
                b|=(1<<(ord(s[k])-ord("a")))
        if dame==1:
            continue
        for k in range(n):
            if (k-i)%2==0 and k>=i and k<=j:
                continue
            if s[k]==' ' or ord(s[k])-ord("a")<0:
                continue
            if b&(1<<(ord(s[k])-ord("a"))):
                dame=1
                break
        if dame==0:
            ok=1
if ok:
    print("Yes")
else:
    print("NO")