#2.
#L=[]
#g=0
#for i in L:
#    g=g+i
#for i in L:
#    if i>(g/len(L)):
#        print(i)
#3.
L=[]
for i in L:
    V=[]
    for k in V:
        if i==k:
            u=0
    V.append(i)
if u==o:
    print('yes')
else:
    print('no')
#6.
#L=[]
#m=i[0]
#for i in L:
#    if i<m:
#        m=i
#        k=0
#for i in L:
#    if (i-m)==5:
#        k=k+1
#print(k)