N = int(input())
data = list(map(int,input().split()))
data = sorted(data)
#print(data)
OK_flg = True
d = data[1]-data[0]
if(d==0):
    OK_flg = False
for i in range(1,len(data)):
    if(d != (data[i] - data[i-1])):
        OK_flg = False
        break
if(OK_flg):
    print("YES")
else:
    print("NO")