a=int(input())
b=[int(i) for i in input().split()]
b.sort()

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