def solve():
    n = int(input())
    xl = sorted([int(i) for i in input().split()])

    # condition 1
    if len(set(xl)) != n:
        print("NO")
        return

    #condition 2
    diff = abs(xl[0] - xl[1])
    for idx in range(1, n):
        if diff != abs(xl[idx-1] - xl[idx]):
            print("NO")
            return
    else:
        print("YES")

if __name__=="__main__":
    solve()