a=int(input())
b=[int(i) for i in input().split()]
b.sort()
c=b[1]-b[0]
if b.count(b[0])>=2:
    print("NO")
else:
    for i in range(1,a):
        d=b[i]-b[i-1]
        if c!=d:
            print("NO")
            break
    else:
        print("YES")