N=int(input())
X=input().split(' ')


Y=[]
for i in range(N):
    Y.append(max(X))
    X.remove(max(X))


d=int(Y[1])-int(Y[0])
if(d==0):
   print('NO')
else:
    for i in range(1,N-1):
        if (d != int(Y[1])-int(Y[0])):
           print('NO')
           break
        if ( i == N-2 ):
           print('YES')