N = int(input())
x = list(map(int, input().split()))
x = sorted(x)

if len(set(x)) != N:
    print('NO')
else:
    a = x.pop(0)
    b = x.pop(0)
    d = b - a
    for c in x:
        if c - b != d:
            print('NO')
            break
        b = c
    else:
        print('YES')