N = int(input())
x = sorted(list(map(int,input().split())))
k = x[1] - x[0]
if k == 0:
    print("NO")
    exit()
for i in range(1,N-1):
    if x[i+1] - x[i] != k:
        print("NO")
        exit()
    else:
        print("YES")