def main():
    N = int(input())
    x = list(map(int, input().split()))
    x.sort()
    dif = []
    for i in range(N-1):
        dif.append(x[i+1] - x[i])
    for j in range(len(dif)-1):
        if dif[j]!=dif[j+1] or dif[j]==0:
            return print('NO')
    return print('YES')
        
if __name__ == '__main__':
    main()