N = int(input())
X = list(map(int, input().split()))
X.sort()
diff = set()
for i in range(N - 1):
    pos, nex = X[i], X[i + 1]
    diff.add(nex - pos)

if 0 in diff:
    print('NO')
else:
    if len(diff) == 1:
        print('YES')
    else:
        print('NO')