n=int(input())
a=sorted(map(int,input().split()))
d=[0]*(n-1)
if len(set(a))==len(a):
    for i in range(1,n):
        d[i-1]=a[i]-a[i-1]
    if len(set(d))==1:
        print('YES')
    else:
        print('NO')
else:
    print('NO')