# No.406 鴨等間隔の法則
n = int(input())
x = [int(i) for i in input().split()]
intervals = [0] * (n - 1)
x.sort()

for i in range(n - 1):
    intervals[i] = x[i + 1] - x[i]

if 0 in intervals:
    print('NO')
elif max(intervals) == min(intervals):
    print('YES')
else:
    print('NO')