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

diff = -1
for i in range(len(x)-1):
    if diff == -1:
        diff = x[i+1]-x[i]
    else:
        if diff != x[i+1]-x[i] or x[i+1]-x[i] == 0:
            print("NO")
            break
else:
    print("YES")