N=int(input())
x=list(map(int,input().split()))

def has_duplicates(seq):
    return len(seq) != len(set(seq))

x.sort()
flag=True
if has_duplicates(x):
    print('NO')
else:
    d=x[1]-x[0]
    for i in range(N-1):
        if x[i+1]-x[i]!=d:
            flag=False
            break
    if flag:
        print('YES')
    else:
        print('NO')