def main():
    N = int(input())
    x = sorted(map(int, input().split(" ")))

    dist = x[1] - x[0]
    for i in range(len(x)-1):
        if x[i] == x[i+1]:
            print("NO")
            return
        tmp = x[i+1] - x[i]
        if dist != tmp:
            print("NO")
            return
        dist = tmp
    print("YES")        

main()