n = int(input())
data = list(map(int, input().split()))
data.sort()
diffs = []

for i in range(1, n):
    diffs.append(data[i-1] - data[i])

diff_1 = diffs[0]
for d in diffs:
    if d != diff_1 or d == 0:
        print("NO")
        break
else:
    print("YES")