N = int(input())
data = list(map(int,input().split(" ")))

if len(set(data)) != len(data):
    print("NO")
else:
    data.sort()
    bit =  data[1] - data[0]
    for i in range(1 , len(data) - 1):
        if data[i] + bit != data[i+1]:
            print("NO")
            break
    else:
        print("YES")