N=int(input())
x=list(map(int,input().split()))
x=sorted(x)
s=x[0+1]-x[0]
n=0

for i in range(1,N-1):
    if s != x[i+1]-x[i] or s == 0:
        n=1
        break
    s=x[i+1]-x[i]

if n == 1:
    print("NO")
else:
    print("YES")