while True:
    try:
        k = input()
        if k.islower() and 1<= len(k) <= 20:
            a = []
            for i in k:
                x = k.count(i)
                a.append(x)
            x = min(a)
            b=[]
            for j in range(len(k)):
                if a[j] == x :
                    b.append(k[j])
            for w in b:
                k = k.replace(w,'')
            print(k)   
    except:
        break